arXiv subjects

Rafael Guzman

Publications and source records attributed to Rafael Guzman.

28 records · Page 2Linked to original sources

arXiv2005

Kinematic Properties and Stellar Populations of Faint Early-Type Galaxies. I. Velocity Dispersion Measurements of Central Coma Galaxies

We present velocity dispersion measurements for 69 faint early-type galaxies in the core of the Coma cluster, spanning -22.0<M_R<-17.5 mag. We examine the L-σrelation for our sample and compare it to that of bright ellipticals from the literature. The distribution of the the faint early-type galaxies in the L-sigma plane follows the relation L ~ σ^{2.01\pm0.36}, which is significantly shallower from L ~ σ^4 as defined for the bright ellipticals. While increased rotational support for fainter early-type galaxies could account for some of the difference in slope, we show that it cannot explain it. We also investigate the Colour-σrelation for our Coma galaxies. Using the scatter in this relation, we constrain the range of galaxy ages as a function of their formation epoch for different formation scenarios. Assuming a strong coordination in the formation epoch of faint early-type systems in Coma, we find that most had to be formed at least 6 Gyrs ago and over a short 1 Gyr period.

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arXiv2005

The DEEP Groth Strip Survey. I. The Sample

The Deep Extragalactic Exploratory Probe (DEEP) is a multi-phase research program dedicated to the study of the formation and evolution of galaxies and of large scale structure in the distant Universe. This paper describes the first five-year phase, denoted DEEP1. A series of ten DEEP1 papers will discuss a range of scientific topics (e.g., the study of photometric and spectral properties of a general distant galaxy survey, the evolution observed in galaxy populations of varied morphologies). The observational basis for these studies is the Groth Survey Strip field, a 127 square arcminute region which has been observed with the Hubble Space Telescope in both broad I-band and V-band optical filters and with the Low Resolution Imaging Spectrograph on the Keck Telescopes. Catalogs of photometric and structural parameters have been constructed for 11,547 galaxies and stars at magnitudes brighter than 29, and spectroscopy has been conducted for a magnitude-color weighted subsample of 818 objects. We evaluate three independent techniques for constructing an imaging catalog for the field from the HST data, and discuss the depth and sampling of the resultant catalogs. The selection of the spectroscopic subsample is discussed, and we describe the multifaceted approach taken to prioritizing objects of interest for a variety of scientific subprograms. A series of Monte Carlo simulations then demonstrates that the spectroscopic subsample can be adequately modeled as a simple function of magnitude and color cuts in the imaging catalog.

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arXiv2005

Are There Local Analogs of Lyman Break Galaxies?

To make direct comparisons in the rest-far-ultraviolet between LBGs at z~3 and more local star-forming galaxies, we use HST/STIS to image a set of 12 nearby (z<0.05) HII galaxies in the FUV and a set of 14 luminous compact blue galaxies (LCBGs) at moderate redshift (z~0.5) in the NUV, corresponding to the rest-FUV. We then subject both sets of galaxy images and those of LBGs at z~3 to the same morphological and structural analysis. We find many qualitative and quantitative similarities between the rest-FUV characteristics of distant LBGs and of the more nearby starburst samples, including general morphologies, sizes, asymmetries, and concentrations. Along with some kinematic similarities, this implies that nearby HII galaxies and LCBGs may be reasonable local analogs of distant Lyman break galaxies.

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arXiv2003

HST detection of spiral structure in two Coma Cluster dwarf galaxies

We report the discovery of (stellar) spiral-like structure in Hubble Space Telescope images of two dwarf galaxies (GMP 3292 and GMP 3629) belonging to the Coma cluster. GMP 3629 is the faintest such galaxy detected in a cluster environment, and it is the first such galaxy observed in the dense Coma cluster. The large bulge and the faintness of the broad spiral-like pattern in GMP 3629 suggests that its disk may have been largely depleted. >We may therefore have found an example of the ``missing link'' in theories of galaxy evolution which have predicted that dwarf spiral galaxies, particularly in clusters, evolve into dwarf elliptical galaxies.

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arXiv2003

The Fundamental Properties of Dwarf Elliptical Galaxies in Clusters

We present preliminary results of an extensive study of the fundamental properties of dwarf elliptical galaxies (dEs) in the Coma cluster. Our study will combine HST surface photometry with ground-based UBRIJK photometry and optical spectroscopy. The combined data set will be used to investigate the intrinsic correlations among global parameters in cluster dEs, including the Fundamental Plane, the color-magnitude relation, the Faber-Jackson and Kormendy relation, and velocity dispersion versus line strength indices. These empirical correlations have provided important constraints to theoretical models of galaxy formation and evolution for "normal" elliptical galaxies. Although dEs are the most abundant galaxy population in clusters their properties remain, however, largely unknown. Our study aims to provide an essential reference for testing current theories on the formation and evolution of dEs in clusters, and understanding their relation to more massive elliptical galaxies.

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arXiv2003

HST photometry of dwarf elliptical galaxies in Coma, and an explanation for the alleged structural dichotomy between dwarf and bright elliptical galaxies

We have analyzed archival HST F606W images of 18 dwarf elliptical (dE) galaxy candidates in the Coma Cluster. We model the full radial extent of their light-profiles by simultaneously fitting a PSF-convolved Sersic R^(1/n) model and, when necessary, either a central point-source or a central PSF-convolved Gaussian. The luminosities of the central component L_nuc scale with the host galaxy luminosity L_gal such that L_nuc = 10^(4.76 +/- 0.10)*(L_gal/10^7)^(0.87 +/- 0.26). The underlying host galaxies display systematic departures from an exponential model that are correlated with the model-independent host galaxy luminosity and are not due to biasing from the nuclear component. The Pearson correlation coefficient between log(n) and central galaxy surface brightness mu_0 (excluding the flux from extraneous central components) is -0.83 at a significance level of 99.99%. The Pearson correlation coefficient between the logarithm of the Sersic index `n' and the host galaxy magnitude is -0.77 at a significance of 99.9%. We explain the observed relationship between dE galaxy luminosity and inner logarithmic profile slope (gamma-prime) as a by-product of the correlation between luminosity and Sersic index n. Including, from the literature, an additional 232 dE and E galaxies spanning 10 mag in absolute magnitude (M), the dE galaxies are shown to display a continuous sequence with the brighter E galaxies such that mu_0 brightens linearly with M until core formation causes the most luminous (M_B < -20.5 mag) E galaxies to deviate from this relation. The different behavior of dE and E galaxies in the M-mu_e (and M- _e) diagram, and the _e-log(R_e) diagram have nothing to do with core formation, and are in fact expected from the continuous and linear relation between M and mu_0 and M and log(n).

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arXiv2001

The Gas Content and Kinematics of Nearby Blue Compact Galaxies: Implications for Studies at Intermediate and High Redshift

We present Arecibo 21 cm spectroscopy, Keck HIRES Hb spectroscopy, and WIYN R-band images of 11 nearby blue compact galaxies selected to be similar to blue compact star-forming galaxies at intermediate redshifts (0.1<z<1). We detect HI in 10 of 11 sample galaxies, yielding HI masses of 0.3-4x10^9 M_odot, HI linewidths, W_20, of 133-249 km/s, dynamical masses of 0.5-5x10^10 M_odot, gas depletion timescales, tau_gas, of 0.3-7 Gyr, HI mass fractions of 0.01-0.58, and mass-to-light ratios of 0.1-0.8. These values span the range typical of nearby HII galaxies, irregulars and spirals. Despite the restricted morphological selection, our sample is quite heterogeneous in HI content, dynamical mass, and gas depletion timescale. Therefore, these galaxies should look very different from each other in 5 Gyr. Fading of intermediate-z luminous blue compact galaxies into NGC-type spheroidals is a viable evolutionary scenario for the least massive, most gas-poor objects. The most consistent characteristic of our sample is that the ratio, R, of HII linewidth to HI 21 cm linewidth (W_20) are systematically less than unity. The simplest explanation is that the ionized gas is more centrally concentrated than the neutral gas within the gravitational potential. On average R=0.66 +/- 0.16, similar to findings for local HII galaxies. We find R is also a function of linewidth; smaller linewidth galaxies have smaller values of R. Correcting optical linewidths by this factor raises derived masses and places these galaxies on the local luminosity--linewidth (Tully-Fisher) relation. If this ratio applies to intermediate-redshift galaxies, then the proposed luminosity evolution of the Tully-Fisher relation is much smaller and more gradual than suggested by studies using optical emission-linewidth measurements.

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arXiv1997

On the Nature of the Strong Emission-Line Galaxies in Cluster Cl 0024+1654: Are Some the Progenitors of Low Mass Spheroidals?

We present new size, line ratio, and velocity width measurements for six strong emission-line galaxies in the galaxy cluster, Cl 0024+1654, at redshift z~0.4. The velocity widths from Keck spectra are all narrow (30<sigma<120 km/s), with three profiles showing double peaks. Four galaxies have low masses (M<10^{10} Mo). Whereas three galaxies were previously reported to be possible AGNs, none exhibit AGN-like emission line ratios or velocity widths. Two or three appear as very blue spirals with the remainder more akin to luminous H-II galaxies undergoing a strong burst of star formation. We propose that after the burst subsides, these galaxies will transform into quiescent dwarfs, and are thus progenitors of some cluster spheroidals (We adopt the nomenclature suggested by Kormendy & Bender (1994), i.e., low-density, dwarf ellipsoidal galaxies like NGC 205 are called `spheroidals' instead of `dwarf ellipticals') seen today.

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arXiv1996

Keck Spectroscopy of Redshift z~3 Galaxies in the Hubble Deep Field

We have obtained spectra with the 10-m Keck telescope of a sample of 24 galaxies having colors consistent with star-forming galaxies at redshifts 2 2. Combined with 5 previously confirmed high-redshift galaxies in the HDF, the 16 confirmed sources yield a comoving volume density of n>2.5^-4 h50^3 Mpc^-3 for q0=0.05, or n>1.2^-3 h50^3 Mpc^-3 for q0=0.5. These densities are comparable to estimates of the local volume density of galaxies brighter than L*, and could be almost three times higher still if all 29 of the unconfirmed candidates in our original sample are indeed also at high redshift. The galaxies are small but luminous, with half-light radii 1.8 < r(1/2) < 6.5 h50^-1 kpc and absolute magnitudes -21.5 > M_B > -23. The HST images show a wide range of morphologies, including several with very close, small knots of emission embedded in wispy extended structures. Using rest-frame UV continuum fluxes with no dust correction, we calculate star formation rates in the range 7 - 24 or 3 - 9 h50^-2 Msun/yr for q0=0.05 and q0=0.5, respectively. The variety of morphologies and the high number density of z=3 galaxies in the HDF suggest that they represent a range of physical processes and stages of galaxy formation and evolution, rather than any one class of object, such as massive ellipticals. A key issue remains the measurement of masses. These high-redshift objects are likely to be the low-mass, starbursting building blocks of more massive galaxies seen today.

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arXiv1996

Redshift z ~ 1 Field Galaxies Observed with the Keck Telescope and the HST

We report results based on 35 new spectroscopic redshifts obtained with the Keck Telescope for field galaxies that also have photometry and morphology from survey images taken by the refurbished HST. A sample of 24 redshifts for galaxies fainter than I = 22 has a median redshift of z ~ 0.81. This result is inconsistent with the lower median redshift of z ~ 0.6 predicted by the ``maximal merger models'' of Carlberg (1996), which otherwise fit existing data. The data match an extrapolation of the CFRS, as well as predictions of certain mild luminosity-evolution models. Nearly half of the redshifts lie in two structures at z ~ 0.81 and z ~ 1.0, showing the presence of high density concentrations spanning scales of ~ 1/h Mpc, i.e., the size of groups. We find emission lines or the presence of possible neighbors in 7 of 9 otherwise luminous galaxies with red central regions at redshifts beyond z ~ 0.7. We also note a diversity of morphological types among blue galaxies at z ~ 1, including small compact galaxies, ``chains,'' and ``blue nucleated galaxies.'' These morphologies are found among local, but generally less luminous, galaxies. Distant blue galaxies also include apparently normal late-type spirals. These findings could imply modest bursts of star formation caused by mergers or interactions of small, gas-rich galaxies with each other or with larger, well-formed galaxies. This first glimpse of very faint z ~ 1 field galaxies of diverse colors and morphologies suggests that a mixture of physical processes is at work in the formation and evolution of faint field galaxies.

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