Near infrared and optical morphology of the dusty galaxy NGC972

Near infrared (NIR) and optical surface photometric analyses of the dusty galaxy NGC972 are presented. The photometric profiles in the BVRJHK bands can be fitted with a combination of gaussian and exponential profiles, corresponding to a starburst nucleus and a stellar disk respectively. The exponential scale length in the B-band is 2.8 times larger than in the K-band, which implies a central B-band optical depth as high as 11. A bulge is absent even in the NIR bands and hence the galaxy must be of a morphological type later than the usually adopted Sb type. Relatively low rotational velocity and high gas content also favor a later type, probably Sd, for the galaxy. Only one arm can be traced in the distribution of old stars; the second arm, however, can be traced in the distribution of dust and HII regions. Data suggest a short NIR bar, which ends inside the nuclear ring. The slowly rising nature of the rotation curve rules out a resonance origin of the the nuclear ring. The ring is most likely not in the plane of the galaxy, given its circular appearance in spite of the moderately high inclination of the galaxy. The off-planar nature of the star forming ring, the unusually high fraction (30%) of the total mass in molecular form, the presence of a nuclear starburst and the asymmetry of spiral arms, are probably the result of a merger with a gas-rich companion galaxy.Comment: Uses aas2pp4.sty and epsfig.sty, 12 pages To appear in Astronomical Journal, October 199

Abundances of CNO elements in z ~ 0.3-0.4 LyC leaking galaxies

We present observations with the Space Telescope Imaging Spectrograph (STIS) onboard the Hubble Space Telescope of eleven Lyman continuum (LyC) leaking galaxies at redshifts, z, in the range 0.29-0.43, with oxygen abundances 12+log(O/H)=7.64-8.16, stellar masses Mstar~10^7.8-10^9.8 Msun and O32=[OIII]5007/[OII]3727 of ~5-20, aiming to detect CIII]1908 emission line. We combine these observations with the optical Sloan Digital Sky Survey (SDSS) spectra for the determination of carbon, nitrogen and oxygen abundances. Our sample was supplemented by thirty one galaxies from the literature, for which carbon, nitrogen and oxygen abundances can be derived from the HST and SDSS spectra. These additional galaxies, however, do not have LyC observations. We find that log(C/O) for the entire sample at 12+log(O/H)<8.1 does not depend on metallicity, with a small dispersion of ~0.13 dex around the average value of ~ -0.75 dex. On the other hand, the log(N/O) in galaxies at z>0.1, including LyC leakers, is systematically higher compared to the rest of the sample with lower metallicity. We find that log(C/O) slightly decreases with increasing Mstar from ~ -0.65 at Mstar=10^6 Msun to ~ -0.80 at Mstar=10^9-10^10 Msun, whereas log(N/O) is considerably enhanced at Mstar>10^8 Msun. The origin of these trends remains basically unknown. One of the possible solutions is to assume that the upper mass limit of the stellar initial mass function (IMF) in more massive galaxies is higher. This would result in higher production of oxygen and larger fraction of massive stars with stellar wind polluting interstellar medium with nitrogen.Comment: 20 pages, 17 figures, accepted for publication in Monthly Notices of the Royal Astronomical Societ

Lyman Break Galaxies Under a Microscope: The Small Scale Dynamics and Mass of an Arc in the Cluster 1E0657-56

Using the near-infrared integral-field spectrograph SPIFFI on the VLT, we have studied the spatially-resolved dynamics in the z=3.2 strongly lensed galaxy 1E0657-56 ``arc+core''. The lensing configuration suggests that the high surface brightness ``core'' is the M=20 magnified central 1 kpc of the galaxy (seen at a spatial resolution of about 200 pc in the source plane), whereas the fainter ``arc'' is a more strongly magnified peripheral region of the same galaxy at about a half-light radius, which otherwise appears to be a typical z=3 Lyman break galaxy. The overall shape of the position-velocity diagram resembles the ``rotation curves'' of the inner few kpcs of nearby L* spiral galaxies. The projected velocities rise rapidly to 75 km/s within the core. This implies a dynamical mass of M_dyn = 10^9.3 M_sun within the central kpc, and suggests that in this system the equivalent of the mass of a present-day L* bulge at the same radius was already in place by z>=3. Approximating the circular velocity of the halo by the measured asymptotic velocity of the rotation curve, we estimate a dark matter halo mass of M_halo = 10^11.7 +/- 0.3, in good agreement with large-scale clustering studies of Lyman break galaxies. The baryonic collapse fraction is low compared to actively star-forming ``BX'' and low-redshift galaxies around z=2, perhaps implying comparatively less gas infall to small radii or efficient feedback. Even more speculatively, the high central mass density might indicate highly dissipative gas collapse in very early stages of galaxy evolution, in approximate agreement with what is expected for ``inside-out'' galaxy formation models.Comment: Accepted for publication in the Astrophysical Journa

Detailed Decomposition of Galaxy Images. II. Beyond Axisymmetric Models

We present a two-dimensional (2-D) fitting algorithm (GALFIT, Version 3) with new capabilities to study the structural components of galaxies and other astronomical objects in digital images. Our technique improves on previous 2-D fitting algorithms by allowing for irregular, curved, logarithmic and power-law spirals, ring and truncated shapes in otherwise traditional parametric functions like the Sersic, Moffat, King, Ferrer, etc., profiles. One can mix and match these new shape features freely, with or without constraints, apply them to an arbitrary number of model components and of numerous profile types, so as to produce realistic-looking galaxy model images. Yet, despite the potential for extreme complexity, the meaning of the key parameters like the Sersic index, effective radius or luminosity remain intuitive and essentially unchanged. The new features have an interesting potential for use to quantify the degree of asymmetry of galaxies, to quantify low surface brightness tidal features beneath and beyond luminous galaxies, to allow more realistic decompositions of galaxy subcomponents in the presence of strong rings and spiral arms, and to enable ways to gauge the uncertainties when decomposing galaxy subcomponents. We illustrate these new features by way of several case studies that display various levels of complexity.Comment: 41 pages, 22 figures, AJ accepted. Minor changes. Full resolution version of this paper is available at: http://users.obs.carnegiescience.edu/peng/work/galfit/galfit3.pd

"Low-state" Black Hole Accretion in Nearby Galaxies

I summarize the main observational properties of low-luminosity AGNs in nearby galaxies to argue that they are the high-mass analogs of black hole X-ray binaries in the "low/hard" state. The principal characteristics of low-state AGNs can be accommodated with a scenario in which the central engine is comprised of three components: an optically thick, geometrically accretion disk with a truncated inner radius, a radiatively inefficient flow, and a compact jet.Comment: 8 pages. To appear in From X-ray Binaries to Quasars: Black Hole Accretion on All Mass Scales, ed. T. J. Maccarone, R. P. Fender, and L. C. Ho (Dordrecht: Kluwer

Stellar and Dust Properties of Local Elliptical Galaxies: Clues to the Onset of Nuclear Activity

We study the stellar and dust properties of a well-defined sample of local elliptical galaxies to investigate the relationship between host galaxy properties and nuclear activity. We select a complete sample of 45 ellipticals from the Palomar spectroscopic survey of nearby galaxies, which includes 20 low-luminosity active galactic nuclei classified as LINERs and 25 inactive galaxies. Using a stellar population synthesis method, we compare the derived stellar population properties of the LINER versus the inactive subsamples. We also study the dust and stellar surface brightness distributions of the central regions of these galaxies using high-resolution images obtained with the {\it Hubble Space Telescope}. Relative to the inactive subsample, ellipticals hosting LINERs share similar total optical and near-infrared luminosity, central stellar velocity dispersions, and nuclear stellar populations as judged from their luminosity-weighted ages and metallicities. LINERs, on the other hand, have a larger fraction of core-type central surface brightness profiles and a much higher frequency of circumnuclear dust structures. Our results support the suggestion that LINERs are powered by low-luminosity AGNs rather than by young or intermediate-age stars. Nuclear activity in nearby elliptical galaxies seems to occur preferentially in those systems where sufficient cold interstellar material has managed to accumulate, perhaps via cooling condensations from hot gas.Comment: 8 pages, accepted by A&

Evolution and Impact of Bars over the Last Eight Billion Years: Early Results from GEMS

Bars drive the dynamical evolution of disk galaxies by redistributing mass and angular momentum, and they are ubiquitous in present-day spirals. Early studies of the Hubble Deep Field reported a dramatic decline in the rest-frame optical bar fraction f_opt to below 5% at redshifts z>0.7, implying that disks at these epochs are fundamentally different from present-day spirals. The GEMS bar project, based on ~8300 galaxies with HST-based morphologies and accurate redshifts over the range 0.2-1.1, aims at constraining the evolution and impact of bars over the last 8 Gyr. We present early results indicating that f_opt remains nearly constant at ~30% over the range z=0.2-1.1,corresponding to lookback times of ~2.5-8 Gyr. The bars detected at z>0.6 are primarily strong with ellipticities of 0.4-0.8. Remarkably, the bar fraction and range of bar sizes observed at z>0.6 appear to be comparable to the values measured in the local Universe for bars of corresponding strengths. Implications for bar evolution models are discussed.Comment: Submitted June 25, 2004. 10 pages 5 figures. To appear in Penetrating Bars through Masks of Cosmic Dust: The Hubble Tuning Fork Strikes a New Note, eds. D. Block, K. Freeman, R. Groess, I. Puerari, & E.K. Block (Dordrecht: Kluwer), in pres