Sandra M. Faber

Publications (6)10.92 Total impact

• Article: The Redshift and Mass Dependence on the Formation of The Hubble Sequence at z>1 from CANDELS/UDS

  Alice Mortlock, Christopher J. Conselice, William G. Hartley, Jamie R. Ownsworth, Caterian Lani, Asa F. L. Bluck, Omar Almaini, Ken Duncan, Arjen van der Wel, Anton M. Koekemoer, Avishai Dekel, Romeel Dave, Harry C. Ferguson, Duilia F. de Mello, Jeffrey A. Newman, Sandra M. Faber, Norman A. Grogin, Dale D. Kocevski, Kamson Lai
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  ABSTRACT: In this paper we present a detailed study of the structures and morphologies of a sample of 1188 massive galaxies with Mstar>10^10Msun between redshifts z=1-3 within the Ultra Deep Survey (UDS) region of the Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey (CANDELS) field. Using this sample we determine how galaxy structure and morphology evolve with time. We visually classify our sample into disks, ellipticals and peculiar systems and correct for redshift effects on our classifications through simulations. We find evolution in the fractions of galaxies at a given visual classification as a function of redshift. The peculiar population is dominant at z>2 with a substantial spheroid population, and a negligible disk population. We compute the transition redshift, ztrans, where the combined fraction of spheroids and disks is equal to that of peculiar galaxies, as ztrans=1.86+/-0.62 for galaxies in our stellar mass range. We find that this changes as a function of stellar mass, with Hubble-type systems becoming dominant at higher redshifts for higher mass galaxies (ztrans=2.22+/-0.82), than for the lower mass galaxies (ztrans=1.73+/-0.57). Higher mass galaxies become morphologically settled before their lower mass counterparts, a form of morphological downsizing. We furthermore compare our visual classifications with Sersic index, the concentration, asymmetry and clumpiness (CAS) parameters, star formation rate and rest frame U-B colour. We find links between the colour of a galaxy, its star formation rate and how extended or peculiar it appears. Finally, we discuss the negligible z>2 disk fraction based on visual morphologies and speculate that this is an effect of forming disks appearing peculiar through processes such as violent disk instabilities or mergers. We conclude that to properly define high redshift morphology a new and more exact classification scheme is needed.
  05/2013;
• Article: The star-forming progenitors of massive red galaxies

  Andrea Cattaneo, Joanna Woo, Avishai Dekel, Sandra M. Faber
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  ABSTRACT: The link between massive red galaxies in the local Universe and star-forming galaxies at high redshift is investigated with a semi-analytic model that has proven successful in many ways, e.g. explaining the galaxy colour-magnitude bimodality and the stellar mass-age relation for red-sequence galaxies. The model is used to explore the processes that drive star formation in different types of galaxies as a function of stellar mass and redshift. We find that most z=2-4 star-forming galaxies with M_*>10^10 M_Sun evolve into red-sequence galaxies. Also, most of the massive galaxies on the red-sequence today have passed through a phase of intense star formation at z>2. Specifically, ~ 90% of today's red galaxies with M_*>10^11 M_Sun were fed during this phase by cold streams including minor mergers. Gas-rich major mergers are rare and the effects of merger-driven starbursts are ephemeral. On the other hand, major mergers are important in powering the most extreme starbursts. Gas-rich mergers also explain the tail of intermediate-mass red galaxies that form relatively late, after the epoch of peak star formation. In two thirds of the currently red galaxies that had an intense star formation event at $z<1$, this event was triggered by a merger.
  01/2013;
• Article: Smooth(er) Stellar Mass Maps in CANDELS: Constraints on the Longevity of Clumps in High-redshift Star-forming Galaxies

  Stijn Wuyts, Natascha M. Forster Schreiber, Reinhard Genzel, Yicheng Guo, Guillermo Barro, Eric F. Bell, Avishai Dekel, Sandra M. Faber, Henry C. Ferguson, Mauro Giavalisco, [......], David C. Koo, Jennifer Lotz, Dieter Lutz, Elizabeth McGrath, Jeffrey A. Newman, David Rosario, Amelie Saintonge, Linda J. Tacconi, Benjamin J. Weiner, Arjen van der Wel
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  ABSTRACT: We perform a detailed analysis of the resolved colors and stellar populations of a complete sample of 323 star-forming galaxies at 0.5 < z < 1.5, and 326 star-forming galaxies at 1.5 < z < 2.5 in the ERS and CANDELS-Deep region of GOODS-South. Galaxies were selected to be more massive than 10^10 Msun and have specific star formation rates above 1/t_H. We model the 7-band optical ACS + near-IR WFC3 spectral energy distributions of individual bins of pixels, accounting simultaneously for the galaxy-integrated photometric constraints available over a longer wavelength range. We analyze variations in rest-frame color, stellar surface mass density, age, and extinction as a function of galactocentric radius and local surface brightness/density, and measure structural parameters on luminosity and stellar mass maps. We find evidence for redder colors, older stellar ages, and increased dust extinction in the nuclei of galaxies. Big star-forming clumps seen in star formation tracers are less prominent or even invisible on the inferred stellar mass distributions. Off-center clumps contribute up to ~20% to the integrated SFR, but only 7% or less to the integrated mass of all massive star-forming galaxies at z ~ 1 and z ~ 2, with the fractional contributions being a decreasing function of wavelength used to select the clumps. The stellar mass profiles tend to have smaller sizes and M20 coefficients, and higher concentration and Gini coefficients than the light distribution. Our results are consistent with an inside-out disk growth scenario with brief (100 - 200 Myr) episodic local enhancements in star formation superposed on the underlying disk. Alternatively, the young ages of off-center clumps may signal inward clump migration, provided this happens efficiently on the order of an orbital timescale.
  03/2012;
• Source

  Available from: ArXiv

  Article: The Nature of Extremely Red H-[4.5]>4 Galaxies revealed with SEDS and CANDELS

  Karina I. Caputi, James S. Dunlop, Ross J. McLure, Jiasheng Huang, Giovanni G. Fazio, Matthew L. N. Ashby, Marco Castellano, Adriano Fontana, Michele Cirasuolo, Omar Almaini, [......], Sandra M. Faber, Henry C. Ferguson, Mauro Giavalisco, Norman A. Grogin, Dale D. Kocevski, Anton M. Koekemoer, David C. Koo, Kamson Lai, Jeffrey A. Newman, Rachel S. Somerville
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  ABSTRACT: We have analysed a sample of 25 extremely red H-[4.5]>4 galaxies, selected using 4.5 micron data from the Spitzer SEDS survey and deep H-band data from the Hubble Space Telescope (HST) CANDELS survey, over ~180 square arcmin of the UKIDSS Ultra Deep Survey (UDS) field. Our aim is to investigate the nature of this rare population of mid-infrared (mid-IR) sources that display such extreme near-to-mid-IR colours. Using up to 17-band photometry (U through 8.0 microns), we have studied in detail their spectral energy distributions, including possible degeneracies in the photometric redshift/internal extinction (zphot-Av) plane. Our sample appears to include sources of very different nature. Between 45% and 75% of them are dust-obscured, massive galaxies at 3<zphot<5. All of the 24 micron-detected sources in our sample are in this category. Two of these have S(24 micron)>300 microJy, which at 3<zphot<5 suggests that they probably host a dust-obscured active galactic nucleus (AGN). Our sample also contains four highly obscured (Av>5) sources at zphot<1. Finally, we analyse in detail two zphot~6 galaxy candidates, and discuss their plausibility and implications. Overall, our red galaxy sample contains the tip of the iceberg of a larger population of z>3 galaxies to be discovered with the future James Webb Space Telescope.
  02/2012;
• Source

  Available from: Mark Mozena

  Article: On the evolution of the velocity–mass–size relations of disc‐dominated galaxies over the past 10 billion years

  Aaron A. Dutton, Frank C. van den Bosch, Sandra M. Faber, Luc Simard, Susan A. Kassin, David C. Koo, Kevin Bundy, Jiasheng Huang, Benjamin J. Weiner, Michael C. Cooper, Jeffrey A. Newman, Mark Mozena, Anton M. Koekemoer
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  ABSTRACT: We study the evolution of the scaling relations between the maximum circular velocity, stellar mass and optical half-light radius of star-forming disc-dominated galaxies in the context of Λ cold dark matter-based galaxy formation models. Using data from the literature combined with new data from the Deep Extragalactic Evolutionary Probe 2 (DEEP2) and All-wavelength Extended Groth Strip International Survey (AEGIS) surveys, we show that there is a consistent picture for the evolution of these scaling relations from z∼ 2 to z= 0, both observationally and theoretically. The evolution of the observed stellar scaling relations is weaker than that of the virial scaling relations of dark matter haloes, which can be reproduced, both qualitatively and quantitatively, with a simple, cosmologically motivated model for disc evolution inside growing Navarro–Frenk–White dark matter haloes. In this model optical half-light radii are smaller, both at fixed stellar mass and at maximum circular velocity, at higher redshifts. This model also predicts that the scaling relations between baryonic quantities (baryonic mass, baryonic half-mass radii and maximum circular velocity) evolve even more weakly than the corresponding stellar relations. We emphasize, though, that this weak evolution does not imply that individual galaxies evolve weakly. On the contrary, individual galaxies grow strongly in mass, size and velocity but in such a way that they move largely along the scaling relations. Finally, recent observations have claimed surprisingly large sizes for a number of star-forming disc galaxies at z≃ 2, which has caused some authors to suggest that high-redshift disc galaxies have abnormally high spin parameters. However, we argue that the disc scalelengths in question have been systematically overestimated by a factor of ∼2 and that there is an offset of a factor of ∼1.4 between Hα sizes and optical sizes. Taking these effects into account, there is no indication that star-forming galaxies at high redshifts (z≃ 2) have abnormally high spin parameters.
  Monthly Notices of the Royal Astronomical Society 01/2011; 410(3):1660 - 1676. · 4.90 Impact Factor
• Source

  Available from: ArXiv

  Article: Evolution of the Stellar Mass Tully-Fisher Relation in Disk Galaxy Merger Simulations

  Matthew D. Covington, Susan A. Kassin, Aaron A. Dutton, Benjamin J. Weiner, Thomas J. Cox, Patrik Jonsson, Joel. R. Primack, Sandra M. Faber, and David C. Koo
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  ABSTRACT: There is a large observational scatter toward low velocities in the stellar mass Tully-Fisher (TF) relation if disturbed and compact objects are included. However, this scatter can be eliminated if one replaces rotation velocity with S 0.5, a quantity that includes a velocity dispersion term added in quadrature with the rotation velocity. In this work, we use a large suite of hydrodynamic N-body galaxy merger simulations to explore a possible mechanism for creating the observed relations. Using mock observations of the simulations, we test for the presence of observational effects and explore the relationship between S 0.5 and intrinsic properties of the galaxies. We find that galaxy mergers can explain the scatter in the TF as well as the tight S 0.5-stellar mass relation. Furthermore, S 0.5 is correlated with the total central mass of a galaxy, including contributions due to dark matter.
  The Astrophysical Journal 01/2010; 710(1):279. · 6.02 Impact Factor