arXiv subjects

Ann Zabludoff

Publications and source records attributed to Ann Zabludoff.

61 records · Page 4Linked to original sources

arXiv2006

E+A Galaxies with Blue Cores: Active Galaxies in Transition

HST ACS images reveal blue cores in four E+A, or post-starburst, galaxies. Follow-up spectroscopy shows that these cores have LINER spectra. The existence of LINERs, consistent with those in many elliptical galaxies, is yet one more piece of evidence that these post-merger, post-starburst, bulge-dominated galaxies will evolve into normal ellipticals. More interestingly, if LINERs are powered by low-luminosity AGN, their presence in these E+As suggests that any rapid growth phase of the central black hole ended in rough concert with the cessation of star formation. This result emphasizes the importance of E+As for exploring how the evolution of black holes and AGN may be tied to that of galactic bulges.

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arXiv2005

Near-infrared imaging of 222 nearby Hdelta-strong galaxies from the SDSS

We present UFTI K-band imaging observations of 222 galaxies that are selected from the Sloan Digital Sky Survey to have unusually strong Hdelta absorption equivalent widths, W(Hd)>4A. Using GIM2D, the images are fit with two-dimensional surface brightness models consisting of a simple disk and bulge component to derive B/T, the fraction of luminosity in the bulge. We find that the galaxies with weak or absent Halpha or [OII] emission (known as k+a galaxies) are predominantly bulge-dominated (with a mode of B/T~0.6), while galaxies with nebular emission (known as e[a] galaxies) are mostly disk-dominated (B/T~0.1). The morphologies and (r-k) colours of most k+a galaxies are inconsistent with the hypothesis that they result from the truncation of star formation in normal, spiral galaxies. However, their (u-g) and (r-k) colours, as well as their Hdelta line strengths, form a sequence that is well matched by a model in which >5 per cent of the stellar mass has been produced in a recent starburst. The lack of scatter in the dust-sensitive (r-k) colours suggests that the unusual spectra of k+a galaxies are not due to the effects of dust. The e(a) galaxies, on the other hand, have a colour distribution that is distinct from the k+a population, and typical of normal or dusty (tauV~2) spiral galaxies. We conclude that many e(a) galaxies are not progenitors of k+a galaxies, but are a separate phenomenon. Both k+a and e(a) galaxies reside in environments (characterized by the local density of galaxies brighter than Mr=-20) that are typical of normal galaxies and that are inconsistent with overdense regions like rich galaxy clusters.

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arXiv2004

Disentangling Morphology, Star Formation, Stellar Mass, and Environment in Galaxy Evolution

We present a study of the spectroscopic and photometric properties of galaxies in six nearby clusters. We perform a partial correlation analysis on our dataset to investigate whether the correlation between star formation rates in galaxies and their environment is merely another aspect of correlations of morphology, stellar mass, or mean stellar age with environment, or whether star formation rates vary independently of these other correlations. We find a residual correlation of ongoing star formation with environment, indicating that even galaxies with similar morphologies, stellar masses, and mean stellar ages have lower star formation rates in denser environments. Thus, the current star formation gradient in clusters is not just another aspect of the morphology-density, stellar mass-density, or mean stellar age-density relations. Furthermore, the star formation gradient cannot be solely the result of initial conditions, but must partly be due to subsequent evolution through a mechanism (or mechanisms) sensitive to environment. Our results constitute a true ``smoking gun'' pointing to the effect of environment on the later evolution of galaxies.

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arXiv2004

Can Early Type Galaxies Evolve from Fading the Disks of Late Types?

We examine whether early-type galaxies in clusters may have evolved from later types by the fading of their disks (e.g., as a result of ram-pressure stripping or strangulation) or by enhancement of the bulge luminosity (e.g., due to tidal interactions and mergers). For this purpose, we compare the bulge and disk luminosities of early- and late-type galaxies and of galaxies at different radial distances from the cluster center. We find that, in order for early-type galaxies, including S0s, to have evolved from late-type galaxies, their bulge luminosities must have been physically enhanced. Disk fading models cannot explain the differences observed. We then show that galaxy bulges are systematically brighter at small projected distances from the cluster center, while disk luminosities are uncorrelated with cluster-centric distance. Our results suggest that bulge enhancement, not disk fading, distinguishes early from late types and is thus at least partially responsible for the morphology-environment relation of bright cluster galaxies.

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arXiv2003

Galaxy Luminosity Functions from Deep Spectroscopic Samples of Rich Clusters

Using a new spectroscopic sample and methods accounting for spectroscopic sampling fractions that vary in magnitude and surface brightness, we present R-band galaxy luminosity functions (GLFs) for six nearby galaxy clusters with redshifts 4000 < cz < 20000 km/s and velocity dispersions 700 < sigma < 1250 km/s. In the case of the nearest cluster, Abell 1060, our sample extends to M_R=-14 (7 magnitudes below M*), making this the deepest spectroscopic determination of the cluster GLF to date. Our methods also yield composite GLFs for cluster and field galaxies to M_R=-17 (M*+4), including the GLFs of subsamples of star forming and quiescent galaxies. The composite GLFs are consistent with Schechter functions (M*_R=-21.14^{+0.17}_{-0.17}, alpha=-1.21^{+0.08}_{-0.07} for the clusters, M*_R=-21.15^{+0.16}_{-0.16}, alpha=-1.28^{+0.12}_{-0.11} for the field). All six cluster samples are individually consistent with the composite GLF down to their respective absolute magnitude limits, but the GLF of the quiescent population in clusters is not universal. There are also significant variations in the GLF of quiescent galaxies between the field and clusters that can be described as a steepening of the faint end slope. The overall GLF in clusters is consistent with that of field galaxies, except for the most luminous tip, which is enhanced in clusters versus the field. The star formation properties of giant galaxies are more strongly correlated with the environment than those of fainter galaxies.

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arXiv2002

Galaxy Star-Formation as a Function of Environment in the Early Data Release of the Sloan Digital Sky Survey

(Abridged) We present in this paper a detailed analysis of the effect of environment on the star-formation activity of galaxies within the EDR of the SDSS. We have used the Halpha emission line to derive the star-formation rate (SFR) for each galaxy within a volume-limited sample of 8598 galaxies with 0.05 < z < 0.095 and M(r)<= -20.45. We find that the SFR of galaxies is strongly correlated with the local (projected) galaxy density and thus we present here the density-SFR relation that is analogous to the density-morphology relation. The effect of density on the SFR of galaxies is seen in three ways. First, the overall distribution of SFRs is shifted to lower values in dense environments compared with the field population. Second, the effect is most noticeable for the strongly star-forming galaxies in the 75th percentile of the SFR distribution. Third, there is a ``break'' (or characteristic density) in the density-SFR relation at a local galaxy density of 1h-2 Mpc-2. To understand this break further, we have studied the SFR of galaxies as a function of clustercentric radius from 17 clusters and groups objectively selected from the SDSS EDR data. The distribution of SFRs of cluster galaxies begins to change, compared with the field population, at a clustercentric radius of 3-4 virial radii, which is consistent with the characteristic break in density that we observe in the density-SFR relation. Our tests suggest that the density-morphology relation alone is unlikely to explain the density-SFR relation we observe. Taken all together, these works demonstrate that the decrease in SFR of galaxies in dense environments is a universal phenomenon over a wide range in density (from 0.08 to 10h-2 Mpc-2) and redshift (out to z = 0.5).

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arXiv2001

The Environmental Dependence of the Infrared Luminosity and Stellar Mass Functions

We investigate the dependence of the galaxy infrared luminosity function (LF) and the associated stellar mass function (SMF) on environment and spectral type using photometry from the Two Micron All Sky Survey and redshifts from the Las Campanas Redshift Survey for galaxies brighter than M_J<-19+5 log h. In the field environment, galaxies with emission lines have LFs with much steeper faint end slopes (alpha_J=-1.39) than galaxies without emission lines (alpha_J=-0.59). In the cluster environment, however, even the non-emission line galaxies have a steep faint-end LF (alpha_J=-1.22). There is also a significant (95%) difference between the overall cluster and field LFs, $Δα_J=-0.34, ΔM_J^\ast=-0.54$. All of these variations are more pronounced in the SMFs, which we compute by relating the strength of the 4000 A break in the optical spectra to a mass-to-light ratio.

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