Ronald O. Marzke

RED NUGGETS AT z ∼ 1.5: COMPACT PASSIVE GALAXIES AND THE FORMATION OF THE KORMENDY RELATION

We present the results of Near-Infrared Camera and Multi-Object Spectrometer (NICMOS) imaging of a sample of 19 high-mass passively evolving galaxies with 1.2 < z < 2, taken primarily from the Gemini Deep Deep Survey (GDDS). Around 80% of galaxies in our GDDS sample have spectra dominated by stars with ages 1 Gyr. Our rest-frame R-band images show that most of these objects have compact regular morphologies which follow the classical R 1/4 law. These galaxies scatter along a tight sequence in the size versus surface brightness parameter space which defines the Kormendy relation. Around one-third (3/10) of the massive red objects in the GDDS sample are extraordinarily compact, with effective radii under 1 kpc. Our NICMOS observations allow the detection of such systems more robustly than is possible with optical (rest-frame UV) data, and while similar systems have been seen at z 2, this is the first time such systems have been detected in a rest-frame optical survey at 1.2 < z < 2. We refer to these compact galaxies as red nuggets, and note that similarly compact massive galaxies are completely absent in the nearby universe. We introduce a new stellar mass Kormendy relation (stellar mass density versus size) which we use to single out the effects of size evolution from those of luminosity and color evolution in stellar populations. The 1 < z < 2 passive galaxies have mass densities that are an order of magnitude larger then early-type galaxies today and are comparable to the compact distant red galaxies at 2 < z < 3. We briefly consider mechanisms for size evolution in contemporary models focusing on equal-mass mergers and adiabatic expansion driven by stellar mass loss. Neither of these mechanisms appears to be able to transform the high-redshift Kormendy relation into its local counterpart, leaving the origin and fate of these compact red nuggets unresolved.

The Galaxy Luminosity Function at z ≤ 0.05: Dependence on Morphology

We investigate the dependence of the local galaxy luminosity function on morphology using 5404 galaxies from the recently enlarged Second Southern Sky Redshift Survey (SSRS2). Over the range -22 ≤ MB ≤ -14 (H0 = 100 km s-1 Mpc-1), the luminosity function of early-type galaxies is well fitted by a Schechter function with parameters M -->*=-19.37 -->−0.11+0.10, α=-1.00 -->−0.09+0.09, and * = 4.4 ± 0.8 × 10-3 Mpc-3. The spiral luminosity function is very similar and is well fitted by the parameters M -->*=-19.43 -->−0.08+0.08, α=-1.11 -->−0.06+0.07, and * = 8.0 ± 1.4 × 10-3 Mpc-3 over the same range in absolute magnitude. The flat faint end of the early-type luminosity function is consistent with earlier measurements from the CfA Redshift Survey (Marzke et al.) but is significantly steeper than the slope measured in the Stromlo-APM survey (Loveday et al.). Combined with the increased normalization of the overall LF measured from intermediate-redshift surveys, the flat faint-end slope of the E/S0 LF produces no-evolution models that reproduce the deep Hubble Space Telescope (HST) counts of early-type galaxies remarkably well. However, the observed normalization of the SSRS2 LF is consistent with the low value measured in other local redshift surveys. The cause of this low-redshift anomaly remains unknown. The luminosity function of irregular and peculiar galaxies in the SSRS2 is very steep: M -->*=-19.78 -->−0.50+0.40, α=-1.81 -->−0.24+0.24, and * = 0.2 ± 0.08 × 10-3 Mpc-3. The steep slope at the faint end is consistent with the LFs measured for Sm-Im galaxies in the CfA survey, UV-selected galaxies (Treyer et al.), star-forming field galaxies (Bromley et al.), and the bluest galaxies in the SSRS2 (Marzke & da Costa). As shown by Driver, Windhorst, & Griffiths, the steep LF reduces the observed excess of faint irregulars over no-evolution predictions but cannot explain it entirely.

Dynamically Close Galaxy Pairs and Merger Rate Evolution in the CNOC2 Redshift Survey

We investigate redshift evolution in the galaxy merger and accretion rates, using a well-defined sample of 4184 galaxies with 0.12 ≤ z ≤ 0.55 and RC ≤ 21.5. We identify 88 galaxies in close (5 ≤ rp ≤ 20 h-1 kpc) dynamical (Δv ≤ 500 km s-1) pairs. These galaxies are used to compute global pair statistics, after accounting for selection effects resulting from the flux limit, k-corrections, luminosity evolution, and spectroscopic incompleteness. We find that the number of companions per galaxy (for -21 ≤ M ≤ -18) is Nc = 0.0321 ± 0.0077 at z = 0.3. The luminosity in companions, per galaxy, is Lc = 0.0294 ± 0.0084 × 1010 h2 L☉. We assume that Nc is proportional to the galaxy merger rate, while Lc is directly related to the mass accretion rate. After increasing the maximum pair separation to 50 h-1 kpc and comparing with the low-redshift SSRS2 pair sample, we infer evolution in the galaxy merger and accretion rates of (1 + z)2.3±0.7 and (1 + z)2.3±0.9, respectively. These are the first such estimates to be made using only confirmed dynamical pairs. When combined with several additional assumptions, this implies that approximately 15% of present epoch galaxies with -21 ≤ MB ≤ -18 have undergone a major merger since z = 1.

The luminosity function for different morphological types in the CfA Redshift Survey

We derive the luminosity function for different morphological types in the original CfA Redshift Survey (CfA1) and in the first two slices of the CfA Redshift Survey Extension (CfA2). CfA1 is a complete sample containing 2397 galaxies distributed over 2.7 steradians with m(sub z) less than or equal 14.5. The first two complete slices of CfA2 contain 1862 galaxies distributed over 0.42 steradians with m(sub z)=15.5. The shapes of the E-S0 and spiral luminosity functions (LF) are indistinguishable. We do not confirm the steeply decreasing faint end in the E-S0 luminosity function found by Loveday et al. for an independent sample in the southern hemisphere. We demonstrate that incomplete classification in deep redshift surveys can lead to underestimates of the faint end of the elliptical luminosity function and could be partially responsible for the difference between the CfA survey and other local field surveys. The faint end of the LF for the Magellanic spirals and irregulars is very steep. The Sm-Im luminosity function is well fit by a Schechter function with M*=-18.79, alpha=-1.87, and phi*=0.6x10(exp -3) for M(sub z) less than or equal to -13. These galaxies are largely responsible for the excess at the faint end of the general CfA luminosity function. The abundance of intrinsically faint, blue galaxies nearby affects the interpretation of deep number counts. The dwarf population increases the expected counts at B=25 in a no-evolution, q(sub 0)=0.05 model by a factor of two over standard no-evolution estimates. These dwarfs change the expected median redshift in deep redshift surveys by less than 10 percent . Thus the steep Sm-Im LF may contribute to the reconciliation of deep number counts with deep redshift surveys.

Evolved Galaxies at z > 1.5 from the Gemini Deep Deep Survey: The Formation Epoch of Massive Stellar Systems

We present spectroscopic evidence from the Gemini Deep Deep Survey for a significant population of color-selected red galaxies at 1.3 1.5 old galaxies have a sky density greater than 0.1 arcmin-2. Conservative age estimates for 20 galaxies with z > 1.3, z = 1.49, give a median age of 1.2 Gyr and zf = 2.4. One-quarter of the galaxies have inferred zf > 4. Models restricted to [Fe/H] ? 0 give median ages and zf of 2.3 Gyr and 3.3, respectively. These galaxies are among the most massive and contribute ~50% of the stellar mass density at 1 < z < 2. The derived ages and most probable star formation histories suggest a high star formation rate (~300-500 M? yr-1) phase in the progenitor population. We argue that most of the red galaxies are not descendants of the typical z ~ 3 Lyman break galaxies. Galaxies associated with luminous submillimeter sources have the requisite star formation rates to be the progenitor population. Our results point toward early and rapid formation for a significant fraction of present-day massive galaxies.

Red nuggets at high redshift: structural evolution of quiescent galaxies over 10 Gyr of cosmic history

We present an analysis of the size growth seen in early-type galaxies over 10 Gyr of cosmic time. Our analysis is based on a homogeneous synthesis of published data from 16 spectroscopic surveys observed at similar spatial resolution, augmented by new measurements for galaxies in the Gemini Deep Deep Survey. In total, our sample contains structural data for 465 galaxies (mainly early-type) in the redshift range 0.2 < z < 2.7. The size evolution of passively evolving galaxies over this redshift range is gradual and continuous, with no evidence for an end or change to the process around z ~ 1, as has been hinted at by some surveys which analyze subsets of the data in isolation. The size growth appears to be independent of stellar mass, with the mass-normalized half-light radius scaling with redshift as Re ∝(1 + z)–1.62 ± 0.34. Surprisingly, this power law seems to be in good agreement with the recently reported continuous size evolution of UV-bright galaxies in the redshift range z ~ 0.5-3.5. It is also in accordance with the predictions from recent theoretical models.

Pairwise velocities of galaxies in the CFA and SSRS2 redshift surveys

(compressed version) We combine the CfA Redshift Survey (CfA2) and the Southern Sky Redshift Survey (SSRS2) to estimate the pairwise velocity dispersion of galaxies

Reconstructing galaxy histories from globular clusters.

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The Las Campanas Infrared Survey. IV. The Photometric Redshift Survey and the Rest-Frame R-Band Galaxy Luminosity Function at 0.5 ≤ z ≤ 1.5

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The Las Campanas Infrared Survey – II. Photometric redshifts, comparison with models and clustering evolution

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