ReadingTimeMachine/rtm-sgt-ocr-v1 · Datasets at Hugging Face

source stringlengths 1 2.05k ⌀	target stringlengths 1 11.7k
SCUBA sources ave therefore candidates to host a population of hiehlv obscured ACNs.	SCUBA sources are therefore candidates to host a population of highly obscured AGNs.
Almaini et al. (1999))	Almaini et al. \cite{almaini99}) )
sueeestOO that. if the SED of high redshift ACN is simular to those observed locally. oue cau explain of the SSCUDA sources at 1 idw.	suggest that, if the SED of high redshift AGN is similar to those observed locally, one can explain of the SCUBA sources at 1 mJy.
This fraction could be significantly higher if à laree population of AGN are Compton thick at N-rav wavelengths.	This fraction could be significantly higher if a large population of AGN are Compton thick at X-ray wavelengths.
Trentham. Blain Coldader (1999)) show that if the SCUBA sources are completely powered by a dust cushrouded ACN then they iav help in explaining the discrepancy between the local density iu super massive black holes aud the lieh redshift AGN component (sce also Fabian Twasawa 1999)).	Trentham, Blain Goldader \cite{trentham}) ) show that if the SCUBA sources are completely powered by a dust enshrouded AGN then they may help in explaining the discrepancy between the local density in super massive black holes and the high redshift AGN component (see also Fabian Iwasawa \cite{fabian99}) ).
Establishing the nature of SCUBA sourees could beD extremelyWwrayhon difficultHMC if theD embeddedDB ACNsUN arepvo likeepo οςSOC[0451915. re.5 completely.Fols obscuredCIO ini alb; directions.vecti: because they would then not be identifiable with the standard optical/IR diagnostics.	Establishing the nature of SCUBA sources could be extremely difficult if the embedded AGNs are like NGC4945, i.e. completely obscured in all directions, because they would then not be identifiable with the standard optical/IR diagnostics.
Iucidlentallv. this fact could possibly account for the sparse detections of type 2 ACNs at high redshifts (Akivama et al. 1999).	Incidentally, this fact could possibly account for the sparse detections of type 2 AGNs at high redshifts (Akiyama et al. \cite{akiyama}) ).
The best possibility for the detection of NGC1915-Ilike ACINs is via their hard X-ray cussion but. uufortunatelv. the sensitivity of existing παν surveys is still. not high cnough to detect high : AGN and the low spatial resolution makes ideutificatious uncertain iu the case of faint optical/ucar-IR counterparts.	The best possibility for the detection of NGC4945-like AGNs is via their hard X-ray emission but, unfortunately, the sensitivity of existing X-ray surveys is still not high enough to detect high $z$ AGN and the low spatial resolution makes identifications uncertain in the case of faint optical/near-IR counterparts.
Moreover. hard N-ravs	Moreover, hard X-rays
extended. a slowly varving evrosvuchrotron source aud a liehh-polarizecdl maser source.	extended, a slowly varying gyrosynchrotron source and a highly-polarized maser source.
Iu the high resolution WLBI data. ouly one poiutlike source is observed.	In the high resolution VLBI data, only one pointlike source is observed.
We identify this as the southern component T Tau Sb.	We identify this as the southern component T Tau Sb.
Tutercoutinental VLA-Effelsbere baselines in the carly part of the experiment allow us to constrain the size of this source to o less than 115 R. in radius.	Intercontinental VLA-Effelsberg baselines in the early part of the experiment allow us to constrain the size of this source to be less than 14.5 $_{\odot}$ in radius.
Circular polarization indicates the Yesenuce of magnetic fields in the source region.	Circular polarization indicates the presence of magnetic fields in the source region.
Short timescale variability is observed. in the form of two distiuct. step-ike fux increases. cach followed by steady imereased dux.	Short timescale variability is observed, in the form of two distinct step-like flux increases, each followed by steady increased flux.
During the first of these. the observed polarization changed from left- to right-handed.	During the first of these, the observed polarization changed from left- to right-handed.
The second seems to rave added ouly rielit-hand polarized flux.	The second seems to have added only right-hand polarized flux.
We argue that lis stronely indicates coherent enüssiou. nost probably an electrou-eyclotron maser.	We argue that this strongly indicates coherent emission, most probably an electron-cyclotron maser.
Based ou this interpretation he magnetic field strength in the maser ciitting region can be estimated to be in the kilogauss range.	Based on this interpretation the magnetic field strength in the maser emitting region can be estimated to be in the kilogauss range.
By areuine that the quiesceut enusslon 1u the fist 6 hours represents evrosvuchrotron cussion frou. rou-therimal electrous and requiring the brightuess eniperature for this cCluission fto lie below scusible inits. we argue that the cmitting magnetic region must ο af least 1 R. in size. and probably larger.	By arguing that the quiescent emission in the first 6 hours represents gyrosynchrotron emission from non-thermal electrons and requiring the brightness temperature for this emission to lie below sensible limits, we argue that the emitting magnetic region must be at least 1 $_{\odot}$ in size, and probably larger.
The evrosvuchrotron endütting regions have sizes of the same order as those expected for an accreting magnuetospliere.	The gyrosynchrotron emitting regions have sizes of the same order as those expected for an accreting magnetosphere.
At low resolutiou the svstem is resolved into the two components. N and ο. T Tau N is consistent with a point source iu our VLA maps.	At low resolution the system is resolved into the two components, N and S. T Tau N is consistent with a point source in our VLA maps.
T Tau S shows evidence of resolved flux. indicating that there is either diffuse enissionu. or additional comiponeuts in the «ποια, or both.	T Tau S shows evidence of resolved flux, indicating that there is either diffuse emission, or additional components in the system, or both.
The nou-detection of T Tau N in the high resolution data indicates that this is a wind source.	The non-detection of T Tau N in the high resolution data indicates that this is a wind source.
The non-detectiou of T Tau Sa iav indicate that this source is below our detection lit. although it is possible that it is resolved out bv our shortest VLBI baseline.	The non-detection of T Tau Sa may indicate that this source is below our detection limit, although it is possible that it is resolved out by our shortest VLBI baseline.
Calmore&Reid(1983) andreferencestherein).. (ey.Majewski2007) —a-cuhan	\citet{Gilmore1983} \citep[for reviews see][and references therein]{Reid1993, Buser1999, Norris1999}, \citep{Robin1996, Ojha2001, Chen2001, Larsen2003}. \citep{Nissen1995, Chiba2000, Gilmore2002, Soubiran2003, Parker2004, Wyse2006}.
ced2005)..	\citep[\egc][]{Reid1993, Chiba2000, Bochanski2007a} $\alpha$.
Moreoever. thin and thick disk attributes are not unique to the Milky Way but a ubiquitous feature for late type galaxies (Dursteim 2007).	Moreoever, thin and thick disk attributes are not unique to the Milky Way but a ubiquitous feature for late type galaxies \citep{Burstein1979, vanderKruit1981, Abe1999, Neeser2002, Yoachim2005, Yoachim2006, Yoachim2007}.
. Receutlv. several SDSSbased. studies have provided further strong observational constraints on the structural. kinematic and chemical properties of stars in the solar cevliuder.	Recently, several SDSS–based studies have provided further strong observational constraints on the structural, kinematic and chemical properties of stars in the solar cylinder.
απόetal.(2008.hereafterJOS) used a photometric parallax method ou SDSS data to estimate distances to ~ LS million stars and studied their spatial distribution.	\citet[hereafter J08]{Juric2008} used a photometric parallax method on SDSS data to estimate distances to $\sim$ 48 million stars and studied their spatial distribution.
Because SDSS provides accurate photometry. which enables reasonably robust distances 15%... Sesaretal. 2008)). as well as faint magnitude limits ἐν< 22) and a laree sky coverage (6500 deg? ). 105 were able to robustly coustrain the parameters of a model for the elobal spatial distribution of stars in the Milky Way.	Because SDSS provides accurate photometry, which enables reasonably robust distances , \citealt{Sesar2008}) ), as well as faint magnitude limits $r<22$ ) and a large sky coverage (6500 $^2$ ), J08 were able to robustly constrain the parameters of a model for the global spatial distribution of stars in the Milky Way.
The JOS model is qualitatively similar to previous work Dalicall&Soncira 1980)) which ideutifies a clear change of slope in the counts of disk stars as a function of distance from the Calactic plane: this changein slope is usually iuterpreted as the transition from the thin to thick disk 2002)..	The J08 model is qualitatively similar to previous work \citealt{Bahcall1980}) ) which identifies a clear change of slope in the counts of disk stars as a function of distance from the Galactic plane; this changein slope is usually interpreted as the transition from the thin to thick disk \citep{Gilmore1983, Siegel2002}. .
Traclitional theories of planetary formation (Safronov 1969) predict that the giant planets form yw accretion of gas outo rocky cores of 5—2084. while lower mass planets form via a clifferent jecliauisin.	Traditional theories of planetary formation (Safronov 1969) predict that the giant planets form by accretion of gas onto rocky cores of $5-20 M_\oplus$, while lower mass planets form via a different mechanism.
Here we evaluate the likelihood for SIM to detect planets with am<p20M	Here we evaluate the likelihood for SIM to detect planets with $m \le 20 M_\oplus$.
[f the primary goal is to detect planets with n:«2OAL. then of the four observing plaus we ave cousidered. the one with 2 µας single measurement. precision is optimal (see 55a) and ‘ould be expected to detect 11-ε or 2549 planets with masses €20M. [or five- ac\| len-year lissions. respectively (see 33 top).	If the primary goal is to detect planets with $m< 20 M_\oplus$, then of the four observing plans we have considered, the one with 2 $\mu$ as single measurement precision is optimal (see 5a) and could be expected to detect $11\pm6$ or $25\pm9$ planets with masses $\le20 M_\oplus$ for five- and ten-year missions, respectively (see 3 top).
A five- or teu-vear mission ix expected to make \|i or 124-6 ass and orbital parameter determinations with accuracy (see 33 middle right) and 323 or 87 mass aud orbital parameter determinatious with accuracy (see 33 bottom right	A five- or ten-year mission is expected to make $4^{+4}_{-3}$ or $12\pm6$ mass and orbital parameter determinations with accuracy (see 3 middle right) and $3\pm3$ or $8^{+5}_{-4}$ mass and orbital parameter determinations with accuracy (see 3 bottom right).
The two-tier strategy would detect. ~5 Or 1TX9 planets with masses aX20M. during a [ive- or ten-year mission. respectively.	The two-tier strategy would detect $\sim5^{+2}_{-3}$ or $\sim17\pm9$ planets with masses $m\le 20 M_\oplus$ during a five- or ten-year mission, respectively.
Lt woulcl measure masses aud orbits with accuracy for ⋅∣ −≻↓≽∩↕⋅↙=6 ⋮↥↽≻↥⋜⋃≺↵↕⊳∖⋜↕∐≼⊔∐≺↵⋜↕⊳∖⋃⋅≺↵↕↕≺↵∐↕⋜↕⊳∖⊳∖≺↵⊳∖⋜↕∐≺⇂∩↓⋅∣≻∐⋜↕↥↥↽≻⋜⋃⋅⋜⋃∐≺↵↕≺↵↕∷∖∖∖↽∐∐∐⋗↸⋰∣⋰∡⋜⊔∙∢∙⇂⊔⋅⋜↕∢∙⊽∖⊽↥∩↓⋅−≻ ⋅↽∣ ⋅⋅∣ Or 9p such planets depending on the length of the mission.	It would measure masses and orbits with accuracy for $2^{+4}_{-2}$ or $7^{+6}_{-5}$ planets and measure the masses and orbital parameters with accuracy for $2^{+3}_{-2}$ or $5^{+5}_{-4}$ such planets depending on the length of the mission.
Again. it is important to remember that these estimates depend on an extrapolation of the planet mass functiou observed for larger masses. although in this case the extrapolation iu mass is relatively small. since radial velocity surveys already detect 3044 plauets.	Again, it is important to remember that these estimates depend on an extrapolation of the planet mass function observed for larger masses, although in this case the extrapolation in mass is relatively small, since radial velocity surveys already detect $\sim30 M_\oplus$ planets.
Auy of the ten-year SIM surveys which we considered is likely to detect oue planet with a mass LAL. for any of the target lists we cousider.	Any of the ten-year SIM surveys which we considered is likely to detect one planet with a mass $\sim1 M_\oplus$, for any of the target lists we consider.
Similarly. a 1 µας five-year SIM survey is likely to detect one planet with a mass LOAL and the other five-year surveys would likely detect one planet with a iass 2—3M. (see Ll aud 10).	Similarly, a 1 $\mu$ as five-year SIM survey is likely to detect one planet with a mass $\sim1.5 M_\oplus$ and the other five-year surveys would likely detect one planet with a mass $\sim2-3M_\oplus$ (see 4 and 10).
Of course. the mass of the smallest planet that SIM will actually detect mmay be siguificantly larger or sinaller than these precictious due to s1nall number statistics and uncertaiuties in the mass function.	Of course, the mass of the smallest planet that SIM will actually detect may be significantly larger or smaller than these predictions due to small number statistics and uncertainties in the mass function.
Either a 1. LoL. or 2 gras survey is likely to measure with accuracy the mass aud orbital parameters of one planet with a imass SAL [or a five-year survey.	Either a 1, 1.4, or 2 $\mu$ as survey is likely to measure with accuracy the mass and orbital parameters of one planet with a mass $\sim5 M_\oplus$ for a five-year survey.
During a ten-year survey. SIM would likely measure with accuracy the mass aid orbital parameters of oue planet with a mass ολ with the 1 µας survey aud ~2À£. with either the l.l or 2 pras surveys.	During a ten-year survey, SIM would likely measure with accuracy the mass and orbital parameters of one planet with a mass $\sim 1.5 M_\oplus$ with the 1 $\mu$ as survey and $\sim2 M_\oplus$ with either the 1.4 or 2 $\mu$ as surveys.
The two-tier strategy would likely measure with accuracy the mass aud orbital parameters of one planet with a mass 2 or L.OAL [or five- or teu-vear surveys.	The two-tier strategy would likely measure with accuracy the mass and orbital parameters of one planet with a mass $\sim5$ or $1.5 M_\oplus$ for five- or ten-year surveys.
be. we create synthetic galaxy images using Lattened Sérrsic profiles with dilferent [lattenings e=1O(1 bfe) and Séresic exponents 7.	be, we create synthetic galaxy images using flattened Sérrsic profiles with different flattenings $\epsilon = 10(1-b/a)$ and Sérrsic exponents $n$.
The hall-light radius is then measured as the geometric mean of the semi-major axis and semi-minor axis of the elliptical isophote that cneloses half the light and by integrating over circular isophotes.	The half-light radius is then measured as the geometric mean of the semi-major axis and semi-minor axis of the elliptical isophote that encloses half the light and by integrating over circular isophotes.
Phe dillerence between the two approaches is plotted. in Fig.	The difference between the two approaches is plotted in Fig.
3. as à function of Hlattening ο anc Sérrsic p.	\ref{fitre} as a function of flattening $\epsilon$ and Sérrsic $n$.
The maximum deviation is obtained for small » and strong [Dattening and is not larger than Aloe(h..)0.15.	The maximum deviation is obtained for small $n$ and strong flattening and is not larger than $\Delta \log({\rm R}_{\rm e}) \approx 0.15$.
his is smaller than the scatter on the observed scaling relations.	This is smaller than the scatter on the observed scaling relations.
We therefore do not expect to see any significant systematic trend of half-light radius with Ilattening as à result of the particular way it was measured.	We therefore do not expect to see any significant systematic trend of half-light radius with flattening as a result of the particular way it was measured.
Although the data show considerable scatter. especially in the cdwarl regime. it is striking that galaxies [rom a wicle range of environments trace a continuous Aly vs. Ry relation over a range οἱ 6 orders of magnitude in luminosity.	Although the data show considerable scatter, especially in the dwarf regime, it is striking that galaxies from a wide range of environments trace a continuous $_V$ vs. $_{\rm e}$ relation over a range of 6 orders of magnitude in luminosity.
]t is well known that earlv-tvpe galaxies brighter than Aly14 mag trace a single Aly vs. 0 relation.	It is well known that early-type galaxies brighter than $_V \sim -14$ mag trace a single $_V$ vs. $n$ relation.
This relation is quantified as log(n)=L4.0.1:Mg by Jerjen&Bingecli (LOOT). as log(n)=Lss\|0.125Mpoocw. by Graham&Guzman (2003).. and as log(n)=1.520.11Mz » Graham&Worley(2008).	This relation is quantified as $\log(n) = -1.4 - 0.1 \times {\rm M}_B$ by \citet{jb97}, as $\log(n) = -1.88 - 0.12 \times {\rm M}_{\rm F606W}$ by \citet{gg03}, and as $\log(n) = -1.52 - 0.11 \times {\rm M}_B$ by \citet{gw08}.
. These authors fit Sérrsic wofiles to the observed surface brightness profiles. evaluated as function of equivalent. radius.	These authors fit Sérrsic profiles to the observed surface brightness profiles, evaluated as function of equivalent radius.
Llowever. it is also possible o fit the growth curve. constructed by integrating a galaxy image over circular apertures. with the growth curve of he Sérrsic profile.	However, it is also possible to fit the growth curve, constructed by integrating a galaxy image over circular apertures, with the growth curve of the Sérrsic profile.
This approach is advocated by	This approach is advocated by
have. until now. prevented detailed studies of HE in the bars of AGN hosts.	have, until now, prevented detailed studies of HI in the bars of AGN hosts.
The ‘fuelling’ of an AGN requires gas from the outer regions of a galaxy to be delivered. to its centre with essentially zero angular momentum. in order to form (ancl refuel) an aceretion cise around a central black hole (Cunn. 1979: Shlosman et abl.	The `fuelling' of an AGN requires gas from the outer regions of a galaxy to be delivered to its centre with essentially zero angular momentum, in order to form (and refuel) an accretion disc around a central black hole (Gunn, 1979; Shlosman et al.,
1990).	1990).
Although. controversial. gas streaming in galactic bars may play an important role in the carly stages of this process (Simkin. Su Schwarz. 1980). with significant angular momentum loss occurring when two different: families of gas orbits meet and. formi. dissipative shocks. allowing gas to move inward (Prendergast. 1983: Athanassoula. 1992a.b).	Although controversial, gas streaming in galactic bars may play an important role in the early stages of this process (Simkin, Su Schwarz, 1980), with significant angular momentum loss occurring when two different families of gas orbits meet and form dissipative shocks, allowing gas to move inward (Prendergast, 1983; Athanassoula, 1992a,b).
Until now. direct evidence for this has been difficult to obtain (Lindblad J6rrsater. LOSS: Sellhvood Wilkinson. 1993: Teuben. 1996) since optical studies are restricted by the small amounts of ionisecl eas in bar shocks (Lindblad et al.	Until now, direct evidence for this has been difficult to obtain (Lindblad Jörrsater, 1988; Sellwood Wilkinson, 1993; Teuben, 1996) since optical studies are restricted by the small amounts of ionised gas in bar shocks (Lindblad et al.,
1996). and. detailed: studies of more ubiquitous neutral hydrogen in the bars of AGN hosts. and indeed. normal galaxies. have been limited by inadequate angular resolution and sensitivity.	1996), and detailed studies of more ubiquitous neutral hydrogen in the bars of AGN hosts, and indeed, normal galaxies, have been limited by inadequate angular resolution and sensitivity.
Although the physical conditions in the host galaxy of an AGN may be intimately related to the nuclear activity. to date there have been relatively lew detailed: synthesis studies of HIE in ACN hosts.	Although the physical conditions in the host galaxy of an AGN may be intimately related to the nuclear activity, to date there have been relatively few detailed synthesis studies of HI in AGN hosts.
As part of an ongoing project to study the distribution and kinematics of HE in AGN (Sevferts) we present here. the highest angular resolution observations of the neutral hydrogen in the bar of the archetypal Sevfert. galaxy NGCAISL. obtained using the VLA in B configuration.	As part of an ongoing project to study the distribution and kinematics of HI in AGN (Seyferts) we present here, the highest angular resolution observations of the neutral hydrogen in the bar of the archetypal Seyfert galaxy NGC4151, obtained using the VLA in B configuration.
NOCAI5I is a woell-studied nearby eas-rich spiral galaxy with a central oval distortion (Bosma. IEkers. Lequeux. 1977) and a Sevfert 1.5 nucleus (Osterbrock Ixoski. 1976).	NGC4151 is a well-studied nearby gas-rich spiral galaxy with a central oval distortion (Bosma, Ekers, Lequeux, 1977) and a Seyfert 1.5 nucleus (Osterbrock Koski, 1976).
Phe oval cistortion. identified kinematically in early LIL stuclies (Bosma et al.	The oval distortion, identified kinematically in early HI studies (Bosma et al.,
1977. Bosma. 1981) and evident in deep optical exposures (Arp. 1977). and. subsequent LIE maps (Pedlar ct al..	1977, Bosma, 1981) and evident in deep optical exposures (Arp, 1977) and subsequent HI maps (Pedlar et al.,
. 1992). is elongated. along. PA ~130° and has dimensions of 3.35«2.1 (12.9 kpe 8.2 kpe).	1992), is elongated along PA $\sim$ $^o$ and has dimensions of $3.3' \times 2.1'$ (12.9 kpc $\times$ 8.2 kpc).
In this paper. we establish the oval distortion as a weak. fat bar and concentrate particularly on the gas dynamics in this region: we relate our study of the gas flows in the bar to models of eas Hows in non-axisvmmoetrie barred. potentials.	In this paper, we establish the oval distortion as a weak, 'fat' bar and concentrate particularly on the gas dynamics in this region; we relate our study of the gas flows in the bar to models of gas flows in non-axisymmetric barred potentials.
Assuming a heliocentric velocity of 998 km +. and Εν = τὸ km \| +. the distance to NGC4ISL is 13.3 Alpe (see also Muncdell et al.	Assuming a heliocentric velocity of 998 km $^{-1}$ , and $_0$ = 75 km $^{-1}$ $^{-1}$, the distance to NGC4151 is 13.3 Mpc (see also Mundell et al.,
1998). so 1 corresponels to 65pc in the galaxy.	1998), so 1" corresponds to 65pc in the galaxy.
Full details of the observations ancl subsequent data processing techniques (including production of the moment maps) are presented in Muncell et al. (	Full details of the observations and subsequent data processing techniques (including production of the moment maps) are presented in Mundell et al. (
1998).	1998).
Ehe data used in this paper were obtained [rom a 63-channel. naturalA weighted spectral line cata cube which has an angular resolution. of ⋅⋅∕∕ ∕∕ à spectral resolution: of ⋅⋅10.3 km s" and a greater sensitivity (lowest detectable column density of⋅⋅⋅ 1.32 x 107"οι em2 7) than the higher. resolution.. uniformly" weighted cube.	The data used in this paper were obtained from a 63-channel, naturally weighted spectral line data cube which has an angular resolution of $'' \times$ $''$, a spectral resolution of 10.3 km $^{-1}$ and a greater sensitivity (lowest detectable column density of 1.32 x $^{20}$ $^{-2}$ ) than the higher resolution, uniformly weighted cube.
NOGC4151 shares some of the basic characteristics of barred spirals as summarised by Roberts et al. (	NGC4151 shares some of the basic characteristics of barred spirals as summarised by Roberts et al. (
1979): for example the “lack of dominance of the bar in photometric studies. which is indeed the case for NGOC4151 where the underlying mass distribution is only a mild. oval distortion. (Bosma et al.	1979); for example the “lack of dominance of the bar in photometric studies”, which is indeed the case for NGC4151 where the underlying mass distribution is only a mild oval distortion (Bosma et al.,
1977: Arp. 1977): the "sharp bend. of the bar into spiral arms” which is evident in the HE image of NOGC4151 (Alundell ct ab.	1977; Arp, 1977); the “sharp bend of the bar into spiral arms” which is evident in the HI image of NGC4151 (Mundell et al.,
1998). and. "gas streaming along the bar (sce Section 3).	1998), and “gas streaming along the bar” (see Section 3).
However. the amount of neutral hydrogen present in the oval region (central 3.3s2.4) of NGCAI5I is unusually high. compared. with other early tvpe barred spirals (e.g. Roberts et al.	However, the amount of neutral hydrogen present in the oval region (central $3.3' \times 2.1'$ ) of NGC4151 is unusually high compared with other early type barred spirals (e.g. Roberts et al.,
1979: Regan et al..	1979; Regan et al.,
. 1996).	1996).
Optical photometry of the outer. spiral structure (Simkin. 1975) found a major axis position angle of 26 and an inclination of 21.	Optical photometry of the outer spiral structure (Simkin, 1975) found a major axis position angle of $\sim$ $^{\circ}$ and an inclination of $^{\circ}$.
Similarly. Peclar et al.	Similarly, Pedlar et al.,
reported thatthe overall LIL velocity field of NCCHI51 was approximately consistent with circular rotation and an inclination of 21 for the galaxy: a change in position angle of the line of nodes in the oval region. however. indicated the presence of non-circular motions.	reported thatthe overall HI velocity field of NGC4151 was approximately consistent with circular rotation and an inclination of $^{\circ}$ for the galaxy; a change in position angle of the line of nodes in the oval region, however, indicated the presence of non-circular motions.
Pheir observations also sugeested structure in the oval but were limited by angular resolution (717"« 22") and the strong central absorption feature.	Their observations also suggested structure in the oval but were limited by angular resolution $\sim17'' \times 22''$ ) and the strong central absorption feature.
They detected regions of high LIL concentration (Nw M15 107 7) inthe north-west and south-cast regions of the bar which appeared to be small spiral arms. with their concave edges facing toward the major axis of the bar (see Section 3.2).	They detected regions of high HI concentration $_H$ $\sim$ 1.5 $\times$ $^{21}$ $^{-2}$ ) in the north-west and south-east regions of the bar which appeared to be small spiral arms, with their concave edges facing toward the major axis of the bar (see Section 3.2).
Ifa uniform circular disc is viewed at. some inclination. i. to the line of sight it appears as an "oval. with a axis. a. and semi-münor axis of (b = a cos i).	If a uniform circular disc is viewed at some inclination, i, to the line of sight it appears as an `oval', with a semi-major axis, a, and semi-minor axis of (b = a cos i).
In the dise is rotating. the tilting of the disc will result in an observed radial velocity field where the zero velocity (or line of constant/svstemic velocity or kinematic minor axis) lies along the spatial minor axis. b. In NGCAISL. the central region is also oval but. the iso-velocity contours are very. cillerent compared. to those expected from an inclined circularly rotating disc.	If the disc is rotating, the tilting of the disc will result in an observed radial velocity field where the zero velocity (or line of constant/systemic velocity or kinematic minor axis) lies along the spatial minor axis, b. In NGC4151, the central region is also oval but the iso-velocity contours are very different compared to those expected from an inclined circularly rotating disc.
The iso-velocity contours are elongated. the oval. indicating he presence of significant deviations from circular motion.	The iso-velocity contours are elongated the oval, indicating the presence of significant deviations from circular motion.
'rendergast (1983) points out that. in barred. galaxies. the gas response leads the bar and so the larger the angle oween the eas (or kinematic) major axis ancl the bar (spatial) major axis. the weaker the bar.	Prendergast (1983) points out that, in barred galaxies, the gas response leads the bar and so the larger the angle between the gas (or kinematic) major axis and the bar (spatial) major axis, the weaker the bar.
For. NGCALSL. assuming the bar lies in the plane of the galaxy ancl taking he average PA of the [ine of nodes in the bar to be 28(Muncdell et al..	For NGC4151, assuming the bar lies in the plane of the galaxy and taking the average PA of the line of nodes in the bar to be $^{\circ}$(Mundell et al.,
1998). this angle is 772. (Le. the kinematic major axis lies almost on the spatial minor axis). indicating	1998), this angle is $\sim$ $^{\circ}$ , (i.e., the kinematic major axis lies almost on the spatial minor axis), indicating
the V I bands.	the V I bands.
We overplotted the errors for all five fields. since the cata were obtained with the same (or similar) exposure times and have similar properties.	We overplotted the errors for all five fields, since the data were obtained with the same (or similar) exposure times and have similar properties.
We have no a priori knowledge of the star-formation history (SEL) o£ CLUVCs.	We have no a priori knowledge of the star-formation history (SFH) of CHVCs.
CLIVCs could have just started to form stars. and then their CALDs would exhibit nothing but the "blue plume”.	CHVCs could have just started to form stars, and then their CMDs would exhibit nothing but the “blue plume".
This seems somewhat unlikely given the non-detection of stellar content. on. survey. plates.	This seems somewhat unlikely given the non-detection of stellar content on survey plates.
LE CIIVCS started to form stars more than a Gyr ago. thew CMDs should exhibit the cred plume”.	If CHVCs started to form stars more than a Gyr ago, their CMDs should exhibit the “red plume".

SCUBA sources ave therefore candidates to host a population of hiehlv obscured ACNs.

SCUBA sources are therefore candidates to host a population of highly obscured AGNs.

Almaini et al. (1999))

Almaini et al. \cite{almaini99}) )

sueeestOO that. if the SED of high redshift ACN is simular to those observed locally. oue cau explain of the SSCUDA sources at 1 idw.

suggest that, if the SED of high redshift AGN is similar to those observed locally, one can explain of the SCUBA sources at 1 mJy.

This fraction could be significantly higher if à laree population of AGN are Compton thick at N-rav wavelengths.

This fraction could be significantly higher if a large population of AGN are Compton thick at X-ray wavelengths.

Trentham. Blain Coldader (1999)) show that if the SCUBA sources are completely powered by a dust cushrouded ACN then they iav help in explaining the discrepancy between the local density iu super massive black holes aud the lieh redshift AGN component (sce also Fabian Twasawa 1999)).

Trentham, Blain Goldader \cite{trentham}) ) show that if the SCUBA sources are completely powered by a dust enshrouded AGN then they may help in explaining the discrepancy between the local density in super massive black holes and the high redshift AGN component (see also Fabian Iwasawa \cite{fabian99}) ).

Establishing the nature of SCUBA sourees could beD extremelyWwrayhon difficultHMC if theD embeddedDB ACNsUN arepvo likeepo οςSOC[0451915. re.5 completely.Fols obscuredCIO ini alb; directions.vecti: because they would then not be identifiable with the standard optical/IR diagnostics.

Establishing the nature of SCUBA sources could be extremely difficult if the embedded AGNs are like NGC4945, i.e. completely obscured in all directions, because they would then not be identifiable with the standard optical/IR diagnostics.

Iucidlentallv. this fact could possibly account for the sparse detections of type 2 ACNs at high redshifts (Akivama et al. 1999).

Incidentally, this fact could possibly account for the sparse detections of type 2 AGNs at high redshifts (Akiyama et al. \cite{akiyama}) ).

The best possibility for the detection of NGC1915-Ilike ACINs is via their hard X-ray cussion but. uufortunatelv. the sensitivity of existing παν surveys is still. not high cnough to detect high : AGN and the low spatial resolution makes ideutificatious uncertain iu the case of faint optical/ucar-IR counterparts.

The best possibility for the detection of NGC4945-like AGNs is via their hard X-ray emission but, unfortunately, the sensitivity of existing X-ray surveys is still not high enough to detect high $z$ AGN and the low spatial resolution makes identifications uncertain in the case of faint optical/near-IR counterparts.

Moreover. hard N-ravs

Moreover, hard X-rays

extended. a slowly varving evrosvuchrotron source aud a liehh-polarizecdl maser source.

extended, a slowly varying gyrosynchrotron source and a highly-polarized maser source.

Iu the high resolution WLBI data. ouly one poiutlike source is observed.

In the high resolution VLBI data, only one pointlike source is observed.

We identify this as the southern component T Tau Sb.

Tutercoutinental VLA-Effelsbere baselines in the carly part of the experiment allow us to constrain the size of this source to o less than 115 R. in radius.

Intercontinental VLA-Effelsberg baselines in the early part of the experiment allow us to constrain the size of this source to be less than 14.5 $_{\odot}$ in radius.

Circular polarization indicates the Yesenuce of magnetic fields in the source region.

Circular polarization indicates the presence of magnetic fields in the source region.

Short timescale variability is observed. in the form of two distiuct. step-ike fux increases. cach followed by steady imereased dux.

Short timescale variability is observed, in the form of two distinct step-like flux increases, each followed by steady increased flux.

During the first of these. the observed polarization changed from left- to right-handed.

During the first of these, the observed polarization changed from left- to right-handed.

The second seems to rave added ouly rielit-hand polarized flux.

The second seems to have added only right-hand polarized flux.

We argue that lis stronely indicates coherent enüssiou. nost probably an electrou-eyclotron maser.

We argue that this strongly indicates coherent emission, most probably an electron-cyclotron maser.

Based ou this interpretation he magnetic field strength in the maser ciitting region can be estimated to be in the kilogauss range.

Based on this interpretation the magnetic field strength in the maser emitting region can be estimated to be in the kilogauss range.

By areuine that the quiesceut enusslon 1u the fist 6 hours represents evrosvuchrotron cussion frou. rou-therimal electrous and requiring the brightuess eniperature for this cCluission fto lie below scusible inits. we argue that the cmitting magnetic region must ο af least 1 R. in size. and probably larger.

By arguing that the quiescent emission in the first 6 hours represents gyrosynchrotron emission from non-thermal electrons and requiring the brightness temperature for this emission to lie below sensible limits, we argue that the emitting magnetic region must be at least 1 $_{\odot}$ in size, and probably larger.

The evrosvuchrotron endütting regions have sizes of the same order as those expected for an accreting magnuetospliere.

The gyrosynchrotron emitting regions have sizes of the same order as those expected for an accreting magnetosphere.

At low resolutiou the svstem is resolved into the two components. N and ο. T Tau N is consistent with a point source iu our VLA maps.

At low resolution the system is resolved into the two components, N and S. T Tau N is consistent with a point source in our VLA maps.

T Tau S shows evidence of resolved flux. indicating that there is either diffuse enissionu. or additional comiponeuts in the «ποια, or both.

T Tau S shows evidence of resolved flux, indicating that there is either diffuse emission, or additional components in the system, or both.

The nou-detection of T Tau N in the high resolution data indicates that this is a wind source.

The non-detection of T Tau N in the high resolution data indicates that this is a wind source.

The non-detectiou of T Tau Sa iav indicate that this source is below our detection lit. although it is possible that it is resolved out bv our shortest VLBI baseline.

The non-detection of T Tau Sa may indicate that this source is below our detection limit, although it is possible that it is resolved out by our shortest VLBI baseline.

Calmore&Reid(1983) andreferencestherein).. (ey.Majewski2007) —a-cuhan

\citet{Gilmore1983} \citep[for reviews see][and references therein]{Reid1993, Buser1999, Norris1999}, \citep{Robin1996, Ojha2001, Chen2001, Larsen2003}. \citep{Nissen1995, Chiba2000, Gilmore2002, Soubiran2003, Parker2004, Wyse2006}.

ced2005)..

\citep[\egc][]{Reid1993, Chiba2000, Bochanski2007a} $\alpha$.

Moreoever. thin and thick disk attributes are not unique to the Milky Way but a ubiquitous feature for late type galaxies (Dursteim 2007).

Moreoever, thin and thick disk attributes are not unique to the Milky Way but a ubiquitous feature for late type galaxies \citep{Burstein1979, vanderKruit1981, Abe1999, Neeser2002, Yoachim2005, Yoachim2006, Yoachim2007}.

. Receutlv. several SDSSbased. studies have provided further strong observational constraints on the structural. kinematic and chemical properties of stars in the solar cevliuder.

Recently, several SDSS–based studies have provided further strong observational constraints on the structural, kinematic and chemical properties of stars in the solar cylinder.

απόetal.(2008.hereafterJOS) used a photometric parallax method ou SDSS data to estimate distances to ~ LS million stars and studied their spatial distribution.

\citet[hereafter J08]{Juric2008} used a photometric parallax method on SDSS data to estimate distances to $\sim$ 48 million stars and studied their spatial distribution.

Because SDSS provides accurate photometry. which enables reasonably robust distances 15%... Sesaretal. 2008)). as well as faint magnitude limits ἐν< 22) and a laree sky coverage (6500 deg? ). 105 were able to robustly coustrain the parameters of a model for the elobal spatial distribution of stars in the Milky Way.

Because SDSS provides accurate photometry, which enables reasonably robust distances , \citealt{Sesar2008}) ), as well as faint magnitude limits $r<22$ ) and a large sky coverage (6500 $^2$ ), J08 were able to robustly constrain the parameters of a model for the global spatial distribution of stars in the Milky Way.

The JOS model is qualitatively similar to previous work Dalicall&Soncira 1980)) which ideutifies a clear change of slope in the counts of disk stars as a function of distance from the Calactic plane: this changein slope is usually iuterpreted as the transition from the thin to thick disk 2002)..

The J08 model is qualitatively similar to previous work \citealt{Bahcall1980}) ) which identifies a clear change of slope in the counts of disk stars as a function of distance from the Galactic plane; this changein slope is usually interpreted as the transition from the thin to thick disk \citep{Gilmore1983, Siegel2002}. .

Traclitional theories of planetary formation (Safronov 1969) predict that the giant planets form yw accretion of gas outo rocky cores of 5—2084. while lower mass planets form via a clifferent jecliauisin.

Traditional theories of planetary formation (Safronov 1969) predict that the giant planets form by accretion of gas onto rocky cores of $5-20 M_\oplus$, while lower mass planets form via a different mechanism.

Here we evaluate the likelihood for SIM to detect planets with am<p20M

Here we evaluate the likelihood for SIM to detect planets with $m \le 20 M_\oplus$.

[f the primary goal is to detect planets with n:«2OAL. then of the four observing plaus we ave cousidered. the one with 2 µας single measurement. precision is optimal (see 55a) and ‘ould be expected to detect 11-ε or 2549 planets with masses €20M. [or five- ac| len-year lissions. respectively (see 33 top).

If the primary goal is to detect planets with $m< 20 M_\oplus$, then of the four observing plans we have considered, the one with 2 $\mu$ as single measurement precision is optimal (see 5a) and could be expected to detect $11\pm6$ or $25\pm9$ planets with masses $\le20 M_\oplus$ for five- and ten-year missions, respectively (see 3 top).

A five- or teu-vear mission ix expected to make |i or 124-6 ass and orbital parameter determinations with accuracy (see 33 middle right) and 323 or 87 mass aud orbital parameter determinatious with accuracy (see 33 bottom right

A five- or ten-year mission is expected to make $4^{+4}_{-3}$ or $12\pm6$ mass and orbital parameter determinations with accuracy (see 3 middle right) and $3\pm3$ or $8^{+5}_{-4}$ mass and orbital parameter determinations with accuracy (see 3 bottom right).

The two-tier strategy would detect. ~5 Or 1TX9 planets with masses aX20M. during a [ive- or ten-year mission. respectively.

The two-tier strategy would detect $\sim5^{+2}_{-3}$ or $\sim17\pm9$ planets with masses $m\le 20 M_\oplus$ during a five- or ten-year mission, respectively.

Lt woulcl measure masses aud orbits with accuracy for ⋅∣ −≻↓≽∩↕⋅↙=6 ⋮↥↽≻↥⋜⋃≺↵↕⊳∖⋜↕∐≼⊔∐≺↵⋜↕⊳∖⋃⋅≺↵↕↕≺↵∐↕⋜↕⊳∖⊳∖≺↵⊳∖⋜↕∐≺⇂∩↓⋅∣≻∐⋜↕↥↥↽≻⋜⋃⋅⋜⋃∐≺↵↕≺↵↕∷∖∖∖↽∐∐∐⋗↸⋰∣⋰∡⋜⊔∙∢∙⇂⊔⋅⋜↕∢∙⊽∖⊽↥∩↓⋅−≻ ⋅↽∣ ⋅⋅∣ Or 9p such planets depending on the length of the mission.

It would measure masses and orbits with accuracy for $2^{+4}_{-2}$ or $7^{+6}_{-5}$ planets and measure the masses and orbital parameters with accuracy for $2^{+3}_{-2}$ or $5^{+5}_{-4}$ such planets depending on the length of the mission.

Again. it is important to remember that these estimates depend on an extrapolation of the planet mass functiou observed for larger masses. although in this case the extrapolation iu mass is relatively small. since radial velocity surveys already detect 3044 plauets.

Again, it is important to remember that these estimates depend on an extrapolation of the planet mass function observed for larger masses, although in this case the extrapolation in mass is relatively small, since radial velocity surveys already detect $\sim30 M_\oplus$ planets.

Auy of the ten-year SIM surveys which we considered is likely to detect oue planet with a mass LAL. for any of the target lists we cousider.

Any of the ten-year SIM surveys which we considered is likely to detect one planet with a mass $\sim1 M_\oplus$, for any of the target lists we consider.

Similarly. a 1 µας five-year SIM survey is likely to detect one planet with a mass LOAL and the other five-year surveys would likely detect one planet with a iass 2—3M. (see Ll aud 10).

Similarly, a 1 $\mu$ as five-year SIM survey is likely to detect one planet with a mass $\sim1.5 M_\oplus$ and the other five-year surveys would likely detect one planet with a mass $\sim2-3M_\oplus$ (see 4 and 10).

Of course. the mass of the smallest planet that SIM will actually detect mmay be siguificantly larger or sinaller than these precictious due to s1nall number statistics and uncertaiuties in the mass function.

Of course, the mass of the smallest planet that SIM will actually detect may be significantly larger or smaller than these predictions due to small number statistics and uncertainties in the mass function.

Either a 1. LoL. or 2 gras survey is likely to measure with accuracy the mass aud orbital parameters of one planet with a imass SAL [or a five-year survey.

Either a 1, 1.4, or 2 $\mu$ as survey is likely to measure with accuracy the mass and orbital parameters of one planet with a mass $\sim5 M_\oplus$ for a five-year survey.

During a ten-year survey. SIM would likely measure with accuracy the mass aid orbital parameters of oue planet with a mass ολ with the 1 µας survey aud ~2À£. with either the l.l or 2 pras surveys.

During a ten-year survey, SIM would likely measure with accuracy the mass and orbital parameters of one planet with a mass $\sim 1.5 M_\oplus$ with the 1 $\mu$ as survey and $\sim2 M_\oplus$ with either the 1.4 or 2 $\mu$ as surveys.

The two-tier strategy would likely measure with accuracy the mass aud orbital parameters of one planet with a mass 2 or L.OAL [or five- or teu-vear surveys.

The two-tier strategy would likely measure with accuracy the mass and orbital parameters of one planet with a mass $\sim5$ or $1.5 M_\oplus$ for five- or ten-year surveys.

be. we create synthetic galaxy images using Lattened Sérrsic profiles with dilferent [lattenings e=1O(1 bfe) and Séresic exponents 7.

be, we create synthetic galaxy images using flattened Sérrsic profiles with different flattenings $\epsilon = 10(1-b/a)$ and Sérrsic exponents $n$.

The hall-light radius is then measured as the geometric mean of the semi-major axis and semi-minor axis of the elliptical isophote that cneloses half the light and by integrating over circular isophotes.

The half-light radius is then measured as the geometric mean of the semi-major axis and semi-minor axis of the elliptical isophote that encloses half the light and by integrating over circular isophotes.

Phe dillerence between the two approaches is plotted. in Fig.

The difference between the two approaches is plotted in Fig.

3. as à function of Hlattening ο anc Sérrsic p.

\ref{fitre} as a function of flattening $\epsilon$ and Sérrsic $n$.

The maximum deviation is obtained for small » and strong [Dattening and is not larger than Aloe(h..)0.15.

The maximum deviation is obtained for small $n$ and strong flattening and is not larger than $\Delta \log({\rm R}_{\rm e}) \approx 0.15$.

his is smaller than the scatter on the observed scaling relations.

This is smaller than the scatter on the observed scaling relations.

We therefore do not expect to see any significant systematic trend of half-light radius with Ilattening as à result of the particular way it was measured.

We therefore do not expect to see any significant systematic trend of half-light radius with flattening as a result of the particular way it was measured.

Although the data show considerable scatter. especially in the cdwarl regime. it is striking that galaxies [rom a wicle range of environments trace a continuous Aly vs. Ry relation over a range οἱ 6 orders of magnitude in luminosity.

Although the data show considerable scatter, especially in the dwarf regime, it is striking that galaxies from a wide range of environments trace a continuous $_V$ vs. $_{\rm e}$ relation over a range of 6 orders of magnitude in luminosity.

]t is well known that earlv-tvpe galaxies brighter than Aly14 mag trace a single Aly vs. 0 relation.

It is well known that early-type galaxies brighter than $_V \sim -14$ mag trace a single $_V$ vs. $n$ relation.

This relation is quantified as log(n)=L4.0.1:Mg by Jerjen&Bingecli (LOOT). as log(n)=Lss|0.125Mpoocw. by Graham&Guzman (2003).. and as log(n)=1.520.11Mz » Graham&Worley(2008).

This relation is quantified as $\log(n) = -1.4 - 0.1 \times {\rm M}_B$ by \citet{jb97}, as $\log(n) = -1.88 - 0.12 \times {\rm M}_{\rm F606W}$ by \citet{gg03}, and as $\log(n) = -1.52 - 0.11 \times {\rm M}_B$ by \citet{gw08}.

. These authors fit Sérrsic wofiles to the observed surface brightness profiles. evaluated as function of equivalent. radius.

These authors fit Sérrsic profiles to the observed surface brightness profiles, evaluated as function of equivalent radius.

Llowever. it is also possible o fit the growth curve. constructed by integrating a galaxy image over circular apertures. with the growth curve of he Sérrsic profile.

However, it is also possible to fit the growth curve, constructed by integrating a galaxy image over circular apertures, with the growth curve of the Sérrsic profile.

This approach is advocated by

have. until now. prevented detailed studies of HE in the bars of AGN hosts.

have, until now, prevented detailed studies of HI in the bars of AGN hosts.

The ‘fuelling’ of an AGN requires gas from the outer regions of a galaxy to be delivered. to its centre with essentially zero angular momentum. in order to form (ancl refuel) an aceretion cise around a central black hole (Cunn. 1979: Shlosman et abl.

The `fuelling' of an AGN requires gas from the outer regions of a galaxy to be delivered to its centre with essentially zero angular momentum, in order to form (and refuel) an accretion disc around a central black hole (Gunn, 1979; Shlosman et al.,

1990).

Although. controversial. gas streaming in galactic bars may play an important role in the carly stages of this process (Simkin. Su Schwarz. 1980). with significant angular momentum loss occurring when two different: families of gas orbits meet and. formi. dissipative shocks. allowing gas to move inward (Prendergast. 1983: Athanassoula. 1992a.b).

Although controversial, gas streaming in galactic bars may play an important role in the early stages of this process (Simkin, Su Schwarz, 1980), with significant angular momentum loss occurring when two different families of gas orbits meet and form dissipative shocks, allowing gas to move inward (Prendergast, 1983; Athanassoula, 1992a,b).

Until now. direct evidence for this has been difficult to obtain (Lindblad J6rrsater. LOSS: Sellhvood Wilkinson. 1993: Teuben. 1996) since optical studies are restricted by the small amounts of ionisecl eas in bar shocks (Lindblad et al.

Until now, direct evidence for this has been difficult to obtain (Lindblad Jörrsater, 1988; Sellwood Wilkinson, 1993; Teuben, 1996) since optical studies are restricted by the small amounts of ionised gas in bar shocks (Lindblad et al.,

1996). and. detailed: studies of more ubiquitous neutral hydrogen in the bars of AGN hosts. and indeed. normal galaxies. have been limited by inadequate angular resolution and sensitivity.

1996), and detailed studies of more ubiquitous neutral hydrogen in the bars of AGN hosts, and indeed, normal galaxies, have been limited by inadequate angular resolution and sensitivity.

Although the physical conditions in the host galaxy of an AGN may be intimately related to the nuclear activity. to date there have been relatively lew detailed: synthesis studies of HIE in ACN hosts.

Although the physical conditions in the host galaxy of an AGN may be intimately related to the nuclear activity, to date there have been relatively few detailed synthesis studies of HI in AGN hosts.

As part of an ongoing project to study the distribution and kinematics of HE in AGN (Sevferts) we present here. the highest angular resolution observations of the neutral hydrogen in the bar of the archetypal Sevfert. galaxy NGCAISL. obtained using the VLA in B configuration.

As part of an ongoing project to study the distribution and kinematics of HI in AGN (Seyferts) we present here, the highest angular resolution observations of the neutral hydrogen in the bar of the archetypal Seyfert galaxy NGC4151, obtained using the VLA in B configuration.

NOCAI5I is a woell-studied nearby eas-rich spiral galaxy with a central oval distortion (Bosma. IEkers. Lequeux. 1977) and a Sevfert 1.5 nucleus (Osterbrock Ixoski. 1976).

NGC4151 is a well-studied nearby gas-rich spiral galaxy with a central oval distortion (Bosma, Ekers, Lequeux, 1977) and a Seyfert 1.5 nucleus (Osterbrock Koski, 1976).

Phe oval cistortion. identified kinematically in early LIL stuclies (Bosma et al.

The oval distortion, identified kinematically in early HI studies (Bosma et al.,

1977. Bosma. 1981) and evident in deep optical exposures (Arp. 1977). and. subsequent LIE maps (Pedlar ct al..

1977, Bosma, 1981) and evident in deep optical exposures (Arp, 1977) and subsequent HI maps (Pedlar et al.,

. 1992). is elongated. along. PA ~130° and has dimensions of 3.35«2.1 (12.9 kpe 8.2 kpe).

1992), is elongated along PA $\sim$ $^o$ and has dimensions of $3.3' \times 2.1'$ (12.9 kpc $\times$ 8.2 kpc).

In this paper. we establish the oval distortion as a weak. fat bar and concentrate particularly on the gas dynamics in this region: we relate our study of the gas flows in the bar to models of eas Hows in non-axisvmmoetrie barred. potentials.

In this paper, we establish the oval distortion as a weak, 'fat' bar and concentrate particularly on the gas dynamics in this region; we relate our study of the gas flows in the bar to models of gas flows in non-axisymmetric barred potentials.

Assuming a heliocentric velocity of 998 km +. and Εν = τὸ km | +. the distance to NGC4ISL is 13.3 Alpe (see also Muncdell et al.

Assuming a heliocentric velocity of 998 km $^{-1}$ , and $_0$ = 75 km $^{-1}$ $^{-1}$, the distance to NGC4151 is 13.3 Mpc (see also Mundell et al.,

1998). so 1 corresponels to 65pc in the galaxy.

1998), so 1" corresponds to 65pc in the galaxy.

Full details of the observations ancl subsequent data processing techniques (including production of the moment maps) are presented in Muncell et al. (

Full details of the observations and subsequent data processing techniques (including production of the moment maps) are presented in Mundell et al. (

1998).

Ehe data used in this paper were obtained [rom a 63-channel. naturalA weighted spectral line cata cube which has an angular resolution. of ⋅⋅∕∕ ∕∕ à spectral resolution: of ⋅⋅10.3 km s" and a greater sensitivity (lowest detectable column density of⋅⋅⋅ 1.32 x 107"οι em2 7) than the higher. resolution.. uniformly" weighted cube.

The data used in this paper were obtained from a 63-channel, naturally weighted spectral line data cube which has an angular resolution of $'' \times$ $''$, a spectral resolution of 10.3 km $^{-1}$ and a greater sensitivity (lowest detectable column density of 1.32 x $^{20}$ $^{-2}$ ) than the higher resolution, uniformly weighted cube.

NOGC4151 shares some of the basic characteristics of barred spirals as summarised by Roberts et al. (

NGC4151 shares some of the basic characteristics of barred spirals as summarised by Roberts et al. (

1979): for example the “lack of dominance of the bar in photometric studies. which is indeed the case for NGOC4151 where the underlying mass distribution is only a mild. oval distortion. (Bosma et al.

1979); for example the “lack of dominance of the bar in photometric studies”, which is indeed the case for NGC4151 where the underlying mass distribution is only a mild oval distortion (Bosma et al.,

1977: Arp. 1977): the "sharp bend. of the bar into spiral arms” which is evident in the HE image of NOGC4151 (Alundell ct ab.

1977; Arp, 1977); the “sharp bend of the bar into spiral arms” which is evident in the HI image of NGC4151 (Mundell et al.,

1998). and. "gas streaming along the bar (sce Section 3).

1998), and “gas streaming along the bar” (see Section 3).

However. the amount of neutral hydrogen present in the oval region (central 3.3s2.4) of NGCAI5I is unusually high. compared. with other early tvpe barred spirals (e.g. Roberts et al.

However, the amount of neutral hydrogen present in the oval region (central $3.3' \times 2.1'$ ) of NGC4151 is unusually high compared with other early type barred spirals (e.g. Roberts et al.,

1979: Regan et al..

1979; Regan et al.,

. 1996).

1996).

Optical photometry of the outer. spiral structure (Simkin. 1975) found a major axis position angle of 26 and an inclination of 21.

Optical photometry of the outer spiral structure (Simkin, 1975) found a major axis position angle of $\sim$ $^{\circ}$ and an inclination of $^{\circ}$.

Similarly. Peclar et al.

Similarly, Pedlar et al.,

reported thatthe overall LIL velocity field of NCCHI51 was approximately consistent with circular rotation and an inclination of 21 for the galaxy: a change in position angle of the line of nodes in the oval region. however. indicated the presence of non-circular motions.

reported thatthe overall HI velocity field of NGC4151 was approximately consistent with circular rotation and an inclination of $^{\circ}$ for the galaxy; a change in position angle of the line of nodes in the oval region, however, indicated the presence of non-circular motions.

Pheir observations also sugeested structure in the oval but were limited by angular resolution (717"« 22") and the strong central absorption feature.

Their observations also suggested structure in the oval but were limited by angular resolution $\sim17'' \times 22''$ ) and the strong central absorption feature.

They detected regions of high LIL concentration (Nw M15 107 7) inthe north-west and south-cast regions of the bar which appeared to be small spiral arms. with their concave edges facing toward the major axis of the bar (see Section 3.2).

They detected regions of high HI concentration $_H$ $\sim$ 1.5 $\times$ $^{21}$ $^{-2}$ ) in the north-west and south-east regions of the bar which appeared to be small spiral arms, with their concave edges facing toward the major axis of the bar (see Section 3.2).

Ifa uniform circular disc is viewed at. some inclination. i. to the line of sight it appears as an "oval. with a axis. a. and semi-münor axis of (b = a cos i).

If a uniform circular disc is viewed at some inclination, i, to the line of sight it appears as an `oval', with a semi-major axis, a, and semi-minor axis of (b = a cos i).

In the dise is rotating. the tilting of the disc will result in an observed radial velocity field where the zero velocity (or line of constant/svstemic velocity or kinematic minor axis) lies along the spatial minor axis. b. In NGCAISL. the central region is also oval but. the iso-velocity contours are very. cillerent compared. to those expected from an inclined circularly rotating disc.

If the disc is rotating, the tilting of the disc will result in an observed radial velocity field where the zero velocity (or line of constant/systemic velocity or kinematic minor axis) lies along the spatial minor axis, b. In NGC4151, the central region is also oval but the iso-velocity contours are very different compared to those expected from an inclined circularly rotating disc.

The iso-velocity contours are elongated. the oval. indicating he presence of significant deviations from circular motion.

The iso-velocity contours are elongated the oval, indicating the presence of significant deviations from circular motion.

'rendergast (1983) points out that. in barred. galaxies. the gas response leads the bar and so the larger the angle oween the eas (or kinematic) major axis ancl the bar (spatial) major axis. the weaker the bar.

Prendergast (1983) points out that, in barred galaxies, the gas response leads the bar and so the larger the angle between the gas (or kinematic) major axis and the bar (spatial) major axis, the weaker the bar.

For. NGCALSL. assuming the bar lies in the plane of the galaxy ancl taking he average PA of the [ine of nodes in the bar to be 28(Muncdell et al..

For NGC4151, assuming the bar lies in the plane of the galaxy and taking the average PA of the line of nodes in the bar to be $^{\circ}$(Mundell et al.,

1998). this angle is 772. (Le. the kinematic major axis lies almost on the spatial minor axis). indicating

1998), this angle is $\sim$ $^{\circ}$ , (i.e., the kinematic major axis lies almost on the spatial minor axis), indicating

the V I bands.

We overplotted the errors for all five fields. since the cata were obtained with the same (or similar) exposure times and have similar properties.

We overplotted the errors for all five fields, since the data were obtained with the same (or similar) exposure times and have similar properties.

We have no a priori knowledge of the star-formation history (SEL) o£ CLUVCs.

We have no a priori knowledge of the star-formation history (SFH) of CHVCs.

CLIVCs could have just started to form stars. and then their CALDs would exhibit nothing but the "blue plume”.

CHVCs could have just started to form stars, and then their CMDs would exhibit nothing but the “blue plume".

This seems somewhat unlikely given the non-detection of stellar content. on. survey. plates.

This seems somewhat unlikely given the non-detection of stellar content on survey plates.

LE CIIVCS started to form stars more than a Gyr ago. thew CMDs should exhibit the cred plume”.

If CHVCs started to form stars more than a Gyr ago, their CMDs should exhibit the “red plume".