Mariska Kriek | UC Berkeley (original) (raw)

Papers by Mariska Kriek

We present Hubble Space Telescope NIC2 morphologies of a spectroscopic sample of massive galaxies... more We present Hubble Space Telescope NIC2 morphologies of a spectroscopic sample of massive galaxies at z~2.3, by extending our sample of 9 compact quiescent galaxies (r_e~0.9 kpc) with 10 massive emission-line galaxies. The emission-line galaxies are classified by the nature of their ionized emission; there are six star-forming galaxies and four galaxies hosting an active galactic nucleus (AGN). The star-forming

One of the most controversial questions regarding the build-up of the stellar content of the univ... more One of the most controversial questions regarding the build-up of the stellar content of the universe is when and how the most massive galaxies formed. Recent studies have found that the number density of the most massive galaxies has evolved little from z=4 to z~1.5, contrary to the predictions from galaxy formation models, with the largest disagreement being at 3<z<4.

The Astrophysical Journal, 2014

ABSTRACT The dense interiors of massive galaxies are among the most intriguing environments in th... more ABSTRACT The dense interiors of massive galaxies are among the most intriguing environments in the Universe. In this paper we ask when these dense cores were formed and determine how galaxies gradually assembled around them. We select galaxies that have a stellar mass &gt;3x10^10 Msun inside r=1 kpc out to z=2.5, using the 3D-HST survey and data at low redshift. The number density of galaxies with dense cores appears to have decreased from z=2.5 to the present, probably at least in part due to stellar mass loss and the resulting adiabatic expansion. We infer that dense cores were mostly formed at z&gt;2.5, consistent with their largely quiescent stellar populations. While the cores appear to form early, the galaxies in which they reside show strong evolution: their total masses increase by a factor of 2-3 from z=2.5 to z=0 and their effective radii increase by a factor of 5-6. As a result, the contribution of dense cores to the total mass of the galaxies in which they reside decreases from ~50% at z=2.5 to ~15% at z=0. Because of their early formation, the contribution of dense cores to the total stellar mass budget of the Universe is a strong function of redshift. The stars in cores with M(1 kpc)&gt;3x10^10 Msun make up ~0.1% of the stellar mass density of the Universe today but 10% - 20% at z=2, depending on their IMF. The formation of these cores required the conversion of ~10^11 Msun of gas into stars within ~1 kpc, while preventing significant star formation at larger radii.

The Astrophysical Journal, 2006

We present first results of a spectroscopic survey targeting K-selected galaxies at z = 2.0 − 2.7... more We present first results of a spectroscopic survey targeting K-selected galaxies at z = 2.0 − 2.7 using the GNIRS instrument on Gemini-South. We obtained near-infrared spectra with a wavelength coverage of 1.0-2.5 µm for 26 K-bright galaxies (K < 19.7) selected from the MUSYC survey using photometric redshifts. We successfully derived spectroscopic redshifts for all 26 galaxies using restframe optical emission lines or the redshifted Balmer/4000Å break. Twenty galaxies have spectroscopic redshifts in the range 2.0 < z < 2.7, for which bright emission lines like Hα and [O iii] fall in atmospheric windows. Surprisingly, we detected no emission lines for nine of these 20 galaxies. The median 2σ upper limit on the rest-frame equivalent width of Hα for these nine galaxies is ∼10Å. The stellar continuum emission of these same nine galaxies is best fitted by evolved stellar population models. The best-fit star formation rate (SFR) is zero for five out of nine galaxies, and consistent with zero within 1σ for the remaining four. Thus, both the Hα measurements and the independent stellar continuum modeling imply that 45% of our K-selected galaxies are not forming stars intensely. This high fraction of galaxies without detected line emission and low SFRs may imply that the suppression of star formation in massive galaxies occurs at higher redshift than is predicted by current CDM galaxy formation models. However, obscured star formation may have been missed, and deep mid-infrared imaging is needed to clarify this situation.

The Astrophysical Journal, 2010

We use the optical to mid-infrared coverage of the NEWFIRM Medium-Band Survey (NMBS) to character... more We use the optical to mid-infrared coverage of the NEWFIRM Medium-Band Survey (NMBS) to characterize, for the first time, the properties of a mass-complete sample of 14 galaxies at 3.0 ≤ z < 4.0 with M star > 2.5 × 10 11 M ⊙ , and to derive significantly more accurate measurements of the high-mass end of the stellar mass function (SMF) of galaxies at 3.0 ≤ z < 4.0. The accurate photometric redshifts and well-sampled SEDs provided by the NMBS combined with the large surveyed area result in significantly reduced contributions from photometric redshift errors and cosmic variance to the total error budget of the SMF. The typical very massive galaxy at 3.0 ≤ z < 4.0 is red and faint in the observer's optical, with a median r-band magnitude of r tot = 26.1, and median rest-frame U − V colors of U − V = 1.6. About 60% of the mass-complete sample have optical colors satisfying either the U-or the B-dropout color criteria, although ∼50% of these galaxies have r > 25.5. We find that ∼30% of the sample has SFRs from SED modeling consistent with zero, although SFRs of up to ∼ 1 − 18 M ⊙ yr −1 are also allowed within 1 σ. However, > 80% of the sample is detected at 24 µm, resulting in total infrared luminosities in the range (0.5-4.0)×10 13 L ⊙ . This implies the presence of either dust-enshrouded starburst activity (with SFRs of 600-4300 M ⊙ yr −1 ) and/or highly-obscured active galactic nuclei (AGN). The contribution of galaxies with M star > 2.5 × 10 11 M ⊙ to the total stellar mass budget at 3.0 ≤ z < 4.0 is ∼ 8 +13 −3 %. Compared to recent estimates of the stellar mass density in galaxies with M star ≈ 10 9 − 10 11 M ⊙ at z ∼ 5 and z ∼ 6, we find an evolution by a factor of 2-7 and 3-22 from z ∼ 5 and z ∼ 6, respectively, to z = 3.5. The previously found disagreement at the high-mass end between observed and modelpredicted SMFs is now significant at the 3 σ level when only random uncertainties are considered. However, systematic uncertainties dominate the total error budget, with errors up to a factor of ∼ 8 in the densities at the high-mass end, bringing the observed SMF in marginal agreement with the predicted SMF. Additional systematic uncertainties on the high-mass end could be potentially introduced by either 1) the intense star-formation and/or the very common AGN activities as inferred from the MIPS 24 µm detections, and/or 2) contamination by a significant population of massive, old, and dusty galaxies at z ∼ 2.6.

The Astrophysical Journal, 2011

We study the evolution of the size -stellar mass relation for a large spectroscopic sample of gal... more We study the evolution of the size -stellar mass relation for a large spectroscopic sample of galaxies in the GOODs North field up to z ∼ 3.5. The sizes of the galaxies are measured from K s -band images (corresponding to rest-frame optical/NIR) from the Subaru 8m telescope. We reproduce earlier results based on photometric redshifts that the sizes of galaxies at a given mass evolve with redshift. Specifically, we compare sizes of UV-bright galaxies at a range of redshifts: Lyman break galaxies (LBGs) selected through the U-drop technique (z ∼ 2.5 − 3.5), BM/BX galaxies at z ∼ 1.5 − 2.5, and GALEX LBGs at low redshift (z ∼ 0.6 − 1.5). The median sizes of these UV-bright galaxies evolve as (1 + z) −1.11±0.13 between z ∼ 0.5 − 3.5. The UV-bright galaxies are significantly larger than quiescent galaxies at the same mass and redshift by 0.45 ± 0.09 dex. We also verify the correlation between color and stellar mass density of galaxies to high redshifts. The sizes of sub-mm galaxies in the same field are measured and compared with BM/BX galaxies. We find that median half-light radii of SMGs is 2.90 ± 0.45 kpc and there is little difference in their size distribution to the UV-bright star forming galaxies.

The Astrophysical Journal, 2011

We present an analysis of the clustering of galaxies as a function of their stellar mass at 1 < z... more We present an analysis of the clustering of galaxies as a function of their stellar mass at 1 < z < 2 using data from the NEWFIRM Medium Band Survey (NMBS). The precise photometric redshifts and stellar masses that the NMBS produces allows us to define a series of stellar mass limited samples of galaxies more massive than 7 × 10 9 M ⊙ , 1 × 10 10 M ⊙ and 3 × 10 10 M ⊙ in three redshift intervals centered on z = 1.1, 1.5 and 1.9 respectively. In each redshift interval we show that there exists a strong dependence of clustering strength on the stellar mass limit of the sample, with more massive galaxies showing a higher clustering amplitude on all scales. We further interpret our clustering measurements in the ΛCDM cosmological context using the halo model of galaxy clustering. We show that the typical halo mass of both central and satellite galaxies increases with stellar mass, whereas the satellite fraction decreases with stellar mass, qualitatively the same as is seen at z < 1. We see little evidence of any redshift dependence in the relationship between stellar mass and halo mass over our narrow redshift range. However, when we compare our measurements with similar ones at z ≃ 0, we see clear evidence for a change in this relation. If we assume a universal baryon fraction, the ratio of stellar mass to halo mass reveals the fraction of baryons that have been converted to stars. We see that the peak in this star formation efficiency for central galaxies shifts to higher halo masses at higher redshift, moving from ≃ 7 × 10 11 h −1 M ⊙ at z ≃ 0 to ≃ 3 × 10 12 h −1 M ⊙ at z ≃ 1.5, revealing evidence of 'halo downsizing'. Finally we show that for highly biased galaxy populations at z > 1 there may be a discrepancy between the space density and clustering predicted by the halo model and the measured clustering and space density. This could imply that there is a problem with one or more ingredient of the halo model at these redshifts, for instance the halo bias relation may not yet be precisely calibrated at high halo masses or galaxies may not be distributed within halos following an NFW profile.

Publications of the Astronomical Society of the Pacific, 2009

Deep near-infrared imaging surveys allow us to select and study distant galaxies in the rest-fram... more Deep near-infrared imaging surveys allow us to select and study distant galaxies in the rest-frame optical, and have transformed our understanding of the early Universe. As the vast majority of K-or IRAC-selected galaxies is too faint for spectroscopy, the interpretation of these surveys relies almost exclusively on photometric redshifts determined from fitting templates to the broad-band photometry. The best-achieved accuracy of these redshifts ∆z/(1 + z) 0.06 at z > 1.5, which is sufficient for determining the broad characteristics of the galaxy population but not for measuring accurate rest-frame colors, stellar population parameters, or the local galaxy density. We have started a near-infrared imaging survey with the NEWFIRM camera on the Kitt Peak 4m telescope to greatly improve the accuracy of photometric redshifts in the range 1.5 z 3.5. The survey uses five medium-bandwidth filters, which provide crude "spectra" over the wavelength range 1 − 1.8 µm for all objects in the 27. ′ 6 × 27. ′ 6 NEWFIRM field. In this first paper, we illustrate the technique by showing medium band NEWFIRM photometry of several galaxies at 1.7 < z < 2.7 from the near-infrared spectroscopic sample of . The filters unambiguously pinpoint the location of the redshifted Balmer break in these galaxies, enabling very accurate redshift measurements. The full survey will provide similar data for ∼ 8000 faint K-selected galaxies at z > 1.5 in the COSMOS and AEGIS fields. The filter set also enables efficient selection of exotic objects such as high redshift quasars, galaxies dominated by emission lines, and very cool brown dwarfs; we show that late T and candidate "Y" dwarfs could be identified using only two of the filters.

Nature, 2009

Recent studies have found that the oldest and most luminous galaxies in the early Universe are su... more Recent studies have found that the oldest and most luminous galaxies in the early Universe are surprisingly compact, 1-7 having stellar masses similar to present-day elliptical galaxies but much smaller sizes. This finding has attracted considerable attention as it suggests that massive galaxies have grown by a factor of ∼ five in size over the past ten billion years. A key test of these results is a determination of the stellar kinematics of one of the compact galaxies: if the sizes of these objects are as extreme as has been claimed, their stars are expected to have much higher velocities than those in present-day galaxies of the same mass. Here we report a measurement of the stellar velocity dispersion of a massive compact galaxy at redshift z = 2.186, corresponding to a look-back time of 10.7 billion years. The velocity dispersion is very high at 510 +165 −95 km s −1 , consistent with the mass and compactness of the galaxy inferred from photometric data and indicating significant recent structural and dynamical evolution of massive galaxies. The uncertainty in the dispersion was determined from simulations which include the effects of noise and template mismatch. However, we caution that some subtle systematic effect may influence the analysis given the low signal-to-noise ratio of our spectrum.

The Astrophysical Journal, 2010

We study the Spitzer Infrared Array Camera (IRAC) mid-infrared (rest-frame optical) fluxes of 14 ... more We study the Spitzer Infrared Array Camera (IRAC) mid-infrared (rest-frame optical) fluxes of 14 newly WFC3/IR-detected z ∼ 7 z 850 −dropout galaxies and 5 z ∼ 8 Y 105 -dropout galaxies. The WFC3/IR depth and spatial resolution allow accurate removal of contaminating foreground light, enabling reliable flux measurements at 3.6µm and 4.5µm. None of the galaxies are detected to [3.6] ≈ 26.9 (AB, 2σ), but a stacking analysis reveals a robust detection for the z 850 -dropouts and an upper limit for the Y 105 −dropouts. We construct average broadband spectral energy distributions using the stacked ACS, WFC3, and IRAC fluxes and fit stellar population synthesis models to derive mean redshifts, stellar masses, and ages. For the z 850 −dropouts, we find z = 6.9 +0.1 −0.1 , (U − V ) rest ≈ 0.4, reddening A V = 0, stellar mass < M * >= 1.2 +0.3 −0.6 ×10 9 M ⊙ (Salpeter initial mass function). The bestfit ages ∼ 300 Myr, M/L V ≈ 0.2, and SSF R ∼ 1.7 Gyr −1 are similar to values reported for luminous z ∼ 7 galaxies, indicating the galaxies are smaller but not much younger. The sub−L * galaxies observed here contribute significantly to the stellar mass density and under favorable conditions may have provided enough photons for sustained reionization at 7 < z < 11. In contrast, the z = 8.3 +0.1 −0.2 Y 105 -dropouts have stellar masses that are uncertain by 1.5 dex due to the near-complete reliance on far-UV data. Adopting the 2σ upper limit on the M/L(z = 8), the stellar mass density to M UV,AB < −18 declines from ρ * (z = 7) = 3.7 +1.4 −1.8 ×10 6 M ⊙ Mpc −3 to ρ * (z = 8) < 8×10 5 M ⊙ Mpc −3 , following ∝ (1 + z) −6 over 3 < z < 8. Lower masses at z = 8 would signify more dramatic evolution, which can be established with deeper IRAC observations, long before the arrival of the James Webb Space Telescope.

The Astrophysical Journal, 2011

We derive stellar masses from SED fitting to rest-frame optical and UV fluxes for 401 star-formin... more We derive stellar masses from SED fitting to rest-frame optical and UV fluxes for 401 star-forming galaxies at z ∼ 4, 5, and 6 from Hubble-WFC3/IR observations of the ERS combined with the deep GOODS-S Spitzer/IRAC data (and include a previously-published z ∼ 7 sample). A massluminosity relation with strongly luminosity-dependent M/L UV ratios is found for the largest sample (299 galaxies) at z ∼ 4. The relation M ∝ L 1.7(±0.2) UV,1500 has a well-determined intrinsic sample variance of 0.5 dex. This relation is also consistent with the more limited samples at z ∼ 5 − 7. This z ∼ 4 mass-luminosity relation, and the well-established faint UV luminosity functions at z ∼ 4 − 7, are used to derive galaxy mass functions (MF) to masses M ∼ 10 8 at z ∼ 4 − 7. A bootstap approach is used to derive the MFs to account for the large scatter in the M-L UV relation and the luminosity function uncertainties, along with an analytical crosscheck. The MFs are also corrected for the effects of incompleteness. The incompleteness-corrected MFs are steeper than previously found, with slopes α M ∼ −1.4 to −1.6 at low masses. These slopes are, however, still substantially flatter than the MFs obtained from recent hydrodynamical simulations. We use these MFs to estimate the stellar mass density (SMD) of the universe to a fixed M UV,AB < −18 as a function of redshift and find a SMD growth ∝ (1+z) −3.4±0.8 from z ∼ 7 to z ∼ 4. We also derive the SMD from the completeness-corrected MFs to a mass limit M ∼ 10 8 M ⊙ . Such completeness-corrected MFs and the derived SMDs will be particularly important for model comparisons as future MFs reach to lower masses.

The Astrophysical Journal, 2013

The Astrophysical Journal Supplement Series, 2009

We present a new, K-selected, optical-to-near infrared photometric catalog of the Extended Chandr... more We present a new, K-selected, optical-to-near infrared photometric catalog of the Extended Chandra Deep Field South (ECDFS), making it publicly available to the astronomical community. 1 The dataset is founded on publicly available imaging, supplemented by original z ′ JK imaging data collected as part of the MUltiwavelength Survey by Yale-Chile (MUSYC). The final photometric catalog consists of photometry derived from U U 38 BV RIz ′ JK imaging covering the full 1 2 × 1 2 • of the ECDFS, plus H band photometry for approximately 80 % of the field. The 5σ flux limit for pointsources is K (AB) tot = 22.0. This is also the nominal completeness and reliability limit of the catalog: the empirical completeness for 21.75 < K < 22.00 is 85 %. We have verified the quality of the catalog through both internal consistency checks, and comparisons to other existing and publicly available catalogs. As well as the photometric catalog, we also present catalogs of photometric redshifts and restframe photometry derived from the ten band photometry. We have collected robust spectroscopic redshift determinations from published sources for 1966 galaxies in the catalog. Based on these sources, we have achieved a (1σ) photometric redshift accuracy of ∆z/(1 + z) = 0.036, with an outlier fraction of 7.8 %. Most of these outliers are X-ray sources. Finally, we describe and release a utility for interpolating restframe photometry from observed SEDs, dubbed InterRest 2 . Particularly in concert with the wealth of already publicly available data in the ECDFS, this new MUSYC catalog provides an excellent resource for studying the changing properties of the massive galaxy population at z 2.

Current observations of the most massive galaxies at 0&amp;amp;amp;amp;amp;amp;amp;amp;amp;am... more Current observations of the most massive galaxies at 0&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;lt;z&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;lt;1 suggest that they evolve very slowly, contrary to expectations from galaxy formation models. Unfortunately it has proven difficult to push these studies to higher redshifts, because broad-band near-infrared surveys do not have the required redshift accuracy. We have recently developed and implemented an extremely efficient technique to measure accurate redshifts of

Hildebrandt et al. (2006A&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp... more Hildebrandt et al. (2006A&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;A...452.1121H) have collected all (up until 2005 December) archival UU38BRVI imaging data taken using the Wide Field Imager (WFI) on the ESO MPG 2.2m telescope. We have supplemented the WFI optical data with original z&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;#39;-band imaging taken using Mosaic-II camera on the CTIO 4m Blanco telescope. The ECDFS data were taken in 2005 January. The new MUSYC

The Astrophysical Journal Supplement Series, 2015

ABSTRACT In this paper we present the MOSFIRE Deep Evolution Field (MOSDEF) survey. The MOSDEF su... more ABSTRACT In this paper we present the MOSFIRE Deep Evolution Field (MOSDEF) survey. The MOSDEF survey aims to obtain moderate-resolution (R=3000-3650) rest-frame optical spectra (~3700-7000 Angstrom) for ~1500 galaxies at 1.37&lt;z&lt;3.80 in three well-studied CANDELS fields: AEGIS, COSMOS, and GOODS-N. Targets are selected in three redshift intervals: 1.37&lt;z&lt;1.70, 2.09&lt;z&lt;2.61, and 2.95&lt;z&lt;3.80, down to fixed H_AB (F160W) magnitudes of 24.0, 24.5 and 25.0, respectively, using the photometric and spectroscopic catalogs from the 3D-HST survey. We target both strong nebular emission lines (e.g., [OII], Hbeta, [OIII], 5008, Halpha, [NII], and [SII]) and stellar continuum and absorption features (e.g., Balmer lines, Ca-II H and K, Mgb, 4000 Angstrom break). Here we present an overview of our survey, the observational strategy, the data reduction and analysis, and the sample characteristics based on spectra obtained during the first 24 nights. To date, we have completed 21 masks, obtaining spectra for 591 galaxies. For ~80% of the targets we identify and measure multiple emission or absorption lines. In addition, we confirm 55 additional galaxies, which were serendipitously detected. The MOSDEF galaxy sample includes unobscured star-forming, dusty star-forming, and quiescent galaxies and spans a wide range in stellar mass (~10^9-10^11.5 Msol) and star formation rate (~0-10^4 Msol/yr). The spectroscopically confirmed sample is roughly representative of an H-band limited galaxy sample at these redshifts. With its large sample size, broad diversity in galaxy properties, and wealth of available ancillary data, MOSDEF will transform our understanding of the stellar, gaseous, metal, dust, and black hole content of galaxies during the time when the universe was most active.

We present Hubble Space Telescope NIC2 morphologies of a spectroscopic sample of massive galaxies... more We present Hubble Space Telescope NIC2 morphologies of a spectroscopic sample of massive galaxies at z~2.3, by extending our sample of 9 compact quiescent galaxies (r_e~0.9 kpc) with 10 massive emission-line galaxies. The emission-line galaxies are classified by the nature of their ionized emission; there are six star-forming galaxies and four galaxies hosting an active galactic nucleus (AGN). The star-forming

One of the most controversial questions regarding the build-up of the stellar content of the univ... more One of the most controversial questions regarding the build-up of the stellar content of the universe is when and how the most massive galaxies formed. Recent studies have found that the number density of the most massive galaxies has evolved little from z=4 to z~1.5, contrary to the predictions from galaxy formation models, with the largest disagreement being at 3<z<4.

The Astrophysical Journal, 2014

ABSTRACT The dense interiors of massive galaxies are among the most intriguing environments in th... more ABSTRACT The dense interiors of massive galaxies are among the most intriguing environments in the Universe. In this paper we ask when these dense cores were formed and determine how galaxies gradually assembled around them. We select galaxies that have a stellar mass &gt;3x10^10 Msun inside r=1 kpc out to z=2.5, using the 3D-HST survey and data at low redshift. The number density of galaxies with dense cores appears to have decreased from z=2.5 to the present, probably at least in part due to stellar mass loss and the resulting adiabatic expansion. We infer that dense cores were mostly formed at z&gt;2.5, consistent with their largely quiescent stellar populations. While the cores appear to form early, the galaxies in which they reside show strong evolution: their total masses increase by a factor of 2-3 from z=2.5 to z=0 and their effective radii increase by a factor of 5-6. As a result, the contribution of dense cores to the total mass of the galaxies in which they reside decreases from ~50% at z=2.5 to ~15% at z=0. Because of their early formation, the contribution of dense cores to the total stellar mass budget of the Universe is a strong function of redshift. The stars in cores with M(1 kpc)&gt;3x10^10 Msun make up ~0.1% of the stellar mass density of the Universe today but 10% - 20% at z=2, depending on their IMF. The formation of these cores required the conversion of ~10^11 Msun of gas into stars within ~1 kpc, while preventing significant star formation at larger radii.

The Astrophysical Journal, 2006

We present first results of a spectroscopic survey targeting K-selected galaxies at z = 2.0 − 2.7... more We present first results of a spectroscopic survey targeting K-selected galaxies at z = 2.0 − 2.7 using the GNIRS instrument on Gemini-South. We obtained near-infrared spectra with a wavelength coverage of 1.0-2.5 µm for 26 K-bright galaxies (K < 19.7) selected from the MUSYC survey using photometric redshifts. We successfully derived spectroscopic redshifts for all 26 galaxies using restframe optical emission lines or the redshifted Balmer/4000Å break. Twenty galaxies have spectroscopic redshifts in the range 2.0 < z < 2.7, for which bright emission lines like Hα and [O iii] fall in atmospheric windows. Surprisingly, we detected no emission lines for nine of these 20 galaxies. The median 2σ upper limit on the rest-frame equivalent width of Hα for these nine galaxies is ∼10Å. The stellar continuum emission of these same nine galaxies is best fitted by evolved stellar population models. The best-fit star formation rate (SFR) is zero for five out of nine galaxies, and consistent with zero within 1σ for the remaining four. Thus, both the Hα measurements and the independent stellar continuum modeling imply that 45% of our K-selected galaxies are not forming stars intensely. This high fraction of galaxies without detected line emission and low SFRs may imply that the suppression of star formation in massive galaxies occurs at higher redshift than is predicted by current CDM galaxy formation models. However, obscured star formation may have been missed, and deep mid-infrared imaging is needed to clarify this situation.

The Astrophysical Journal, 2010

We use the optical to mid-infrared coverage of the NEWFIRM Medium-Band Survey (NMBS) to character... more We use the optical to mid-infrared coverage of the NEWFIRM Medium-Band Survey (NMBS) to characterize, for the first time, the properties of a mass-complete sample of 14 galaxies at 3.0 ≤ z < 4.0 with M star > 2.5 × 10 11 M ⊙ , and to derive significantly more accurate measurements of the high-mass end of the stellar mass function (SMF) of galaxies at 3.0 ≤ z < 4.0. The accurate photometric redshifts and well-sampled SEDs provided by the NMBS combined with the large surveyed area result in significantly reduced contributions from photometric redshift errors and cosmic variance to the total error budget of the SMF. The typical very massive galaxy at 3.0 ≤ z < 4.0 is red and faint in the observer's optical, with a median r-band magnitude of r tot = 26.1, and median rest-frame U − V colors of U − V = 1.6. About 60% of the mass-complete sample have optical colors satisfying either the U-or the B-dropout color criteria, although ∼50% of these galaxies have r > 25.5. We find that ∼30% of the sample has SFRs from SED modeling consistent with zero, although SFRs of up to ∼ 1 − 18 M ⊙ yr −1 are also allowed within 1 σ. However, > 80% of the sample is detected at 24 µm, resulting in total infrared luminosities in the range (0.5-4.0)×10 13 L ⊙ . This implies the presence of either dust-enshrouded starburst activity (with SFRs of 600-4300 M ⊙ yr −1 ) and/or highly-obscured active galactic nuclei (AGN). The contribution of galaxies with M star > 2.5 × 10 11 M ⊙ to the total stellar mass budget at 3.0 ≤ z < 4.0 is ∼ 8 +13 −3 %. Compared to recent estimates of the stellar mass density in galaxies with M star ≈ 10 9 − 10 11 M ⊙ at z ∼ 5 and z ∼ 6, we find an evolution by a factor of 2-7 and 3-22 from z ∼ 5 and z ∼ 6, respectively, to z = 3.5. The previously found disagreement at the high-mass end between observed and modelpredicted SMFs is now significant at the 3 σ level when only random uncertainties are considered. However, systematic uncertainties dominate the total error budget, with errors up to a factor of ∼ 8 in the densities at the high-mass end, bringing the observed SMF in marginal agreement with the predicted SMF. Additional systematic uncertainties on the high-mass end could be potentially introduced by either 1) the intense star-formation and/or the very common AGN activities as inferred from the MIPS 24 µm detections, and/or 2) contamination by a significant population of massive, old, and dusty galaxies at z ∼ 2.6.

The Astrophysical Journal, 2011

We study the evolution of the size -stellar mass relation for a large spectroscopic sample of gal... more We study the evolution of the size -stellar mass relation for a large spectroscopic sample of galaxies in the GOODs North field up to z ∼ 3.5. The sizes of the galaxies are measured from K s -band images (corresponding to rest-frame optical/NIR) from the Subaru 8m telescope. We reproduce earlier results based on photometric redshifts that the sizes of galaxies at a given mass evolve with redshift. Specifically, we compare sizes of UV-bright galaxies at a range of redshifts: Lyman break galaxies (LBGs) selected through the U-drop technique (z ∼ 2.5 − 3.5), BM/BX galaxies at z ∼ 1.5 − 2.5, and GALEX LBGs at low redshift (z ∼ 0.6 − 1.5). The median sizes of these UV-bright galaxies evolve as (1 + z) −1.11±0.13 between z ∼ 0.5 − 3.5. The UV-bright galaxies are significantly larger than quiescent galaxies at the same mass and redshift by 0.45 ± 0.09 dex. We also verify the correlation between color and stellar mass density of galaxies to high redshifts. The sizes of sub-mm galaxies in the same field are measured and compared with BM/BX galaxies. We find that median half-light radii of SMGs is 2.90 ± 0.45 kpc and there is little difference in their size distribution to the UV-bright star forming galaxies.

The Astrophysical Journal, 2011

We present an analysis of the clustering of galaxies as a function of their stellar mass at 1 < z... more We present an analysis of the clustering of galaxies as a function of their stellar mass at 1 < z < 2 using data from the NEWFIRM Medium Band Survey (NMBS). The precise photometric redshifts and stellar masses that the NMBS produces allows us to define a series of stellar mass limited samples of galaxies more massive than 7 × 10 9 M ⊙ , 1 × 10 10 M ⊙ and 3 × 10 10 M ⊙ in three redshift intervals centered on z = 1.1, 1.5 and 1.9 respectively. In each redshift interval we show that there exists a strong dependence of clustering strength on the stellar mass limit of the sample, with more massive galaxies showing a higher clustering amplitude on all scales. We further interpret our clustering measurements in the ΛCDM cosmological context using the halo model of galaxy clustering. We show that the typical halo mass of both central and satellite galaxies increases with stellar mass, whereas the satellite fraction decreases with stellar mass, qualitatively the same as is seen at z < 1. We see little evidence of any redshift dependence in the relationship between stellar mass and halo mass over our narrow redshift range. However, when we compare our measurements with similar ones at z ≃ 0, we see clear evidence for a change in this relation. If we assume a universal baryon fraction, the ratio of stellar mass to halo mass reveals the fraction of baryons that have been converted to stars. We see that the peak in this star formation efficiency for central galaxies shifts to higher halo masses at higher redshift, moving from ≃ 7 × 10 11 h −1 M ⊙ at z ≃ 0 to ≃ 3 × 10 12 h −1 M ⊙ at z ≃ 1.5, revealing evidence of 'halo downsizing'. Finally we show that for highly biased galaxy populations at z > 1 there may be a discrepancy between the space density and clustering predicted by the halo model and the measured clustering and space density. This could imply that there is a problem with one or more ingredient of the halo model at these redshifts, for instance the halo bias relation may not yet be precisely calibrated at high halo masses or galaxies may not be distributed within halos following an NFW profile.

Publications of the Astronomical Society of the Pacific, 2009

Deep near-infrared imaging surveys allow us to select and study distant galaxies in the rest-fram... more Deep near-infrared imaging surveys allow us to select and study distant galaxies in the rest-frame optical, and have transformed our understanding of the early Universe. As the vast majority of K-or IRAC-selected galaxies is too faint for spectroscopy, the interpretation of these surveys relies almost exclusively on photometric redshifts determined from fitting templates to the broad-band photometry. The best-achieved accuracy of these redshifts ∆z/(1 + z) 0.06 at z > 1.5, which is sufficient for determining the broad characteristics of the galaxy population but not for measuring accurate rest-frame colors, stellar population parameters, or the local galaxy density. We have started a near-infrared imaging survey with the NEWFIRM camera on the Kitt Peak 4m telescope to greatly improve the accuracy of photometric redshifts in the range 1.5 z 3.5. The survey uses five medium-bandwidth filters, which provide crude "spectra" over the wavelength range 1 − 1.8 µm for all objects in the 27. ′ 6 × 27. ′ 6 NEWFIRM field. In this first paper, we illustrate the technique by showing medium band NEWFIRM photometry of several galaxies at 1.7 < z < 2.7 from the near-infrared spectroscopic sample of . The filters unambiguously pinpoint the location of the redshifted Balmer break in these galaxies, enabling very accurate redshift measurements. The full survey will provide similar data for ∼ 8000 faint K-selected galaxies at z > 1.5 in the COSMOS and AEGIS fields. The filter set also enables efficient selection of exotic objects such as high redshift quasars, galaxies dominated by emission lines, and very cool brown dwarfs; we show that late T and candidate "Y" dwarfs could be identified using only two of the filters.

Nature, 2009

Recent studies have found that the oldest and most luminous galaxies in the early Universe are su... more Recent studies have found that the oldest and most luminous galaxies in the early Universe are surprisingly compact, 1-7 having stellar masses similar to present-day elliptical galaxies but much smaller sizes. This finding has attracted considerable attention as it suggests that massive galaxies have grown by a factor of ∼ five in size over the past ten billion years. A key test of these results is a determination of the stellar kinematics of one of the compact galaxies: if the sizes of these objects are as extreme as has been claimed, their stars are expected to have much higher velocities than those in present-day galaxies of the same mass. Here we report a measurement of the stellar velocity dispersion of a massive compact galaxy at redshift z = 2.186, corresponding to a look-back time of 10.7 billion years. The velocity dispersion is very high at 510 +165 −95 km s −1 , consistent with the mass and compactness of the galaxy inferred from photometric data and indicating significant recent structural and dynamical evolution of massive galaxies. The uncertainty in the dispersion was determined from simulations which include the effects of noise and template mismatch. However, we caution that some subtle systematic effect may influence the analysis given the low signal-to-noise ratio of our spectrum.

The Astrophysical Journal, 2010

We study the Spitzer Infrared Array Camera (IRAC) mid-infrared (rest-frame optical) fluxes of 14 ... more We study the Spitzer Infrared Array Camera (IRAC) mid-infrared (rest-frame optical) fluxes of 14 newly WFC3/IR-detected z ∼ 7 z 850 −dropout galaxies and 5 z ∼ 8 Y 105 -dropout galaxies. The WFC3/IR depth and spatial resolution allow accurate removal of contaminating foreground light, enabling reliable flux measurements at 3.6µm and 4.5µm. None of the galaxies are detected to [3.6] ≈ 26.9 (AB, 2σ), but a stacking analysis reveals a robust detection for the z 850 -dropouts and an upper limit for the Y 105 −dropouts. We construct average broadband spectral energy distributions using the stacked ACS, WFC3, and IRAC fluxes and fit stellar population synthesis models to derive mean redshifts, stellar masses, and ages. For the z 850 −dropouts, we find z = 6.9 +0.1 −0.1 , (U − V ) rest ≈ 0.4, reddening A V = 0, stellar mass < M * >= 1.2 +0.3 −0.6 ×10 9 M ⊙ (Salpeter initial mass function). The bestfit ages ∼ 300 Myr, M/L V ≈ 0.2, and SSF R ∼ 1.7 Gyr −1 are similar to values reported for luminous z ∼ 7 galaxies, indicating the galaxies are smaller but not much younger. The sub−L * galaxies observed here contribute significantly to the stellar mass density and under favorable conditions may have provided enough photons for sustained reionization at 7 < z < 11. In contrast, the z = 8.3 +0.1 −0.2 Y 105 -dropouts have stellar masses that are uncertain by 1.5 dex due to the near-complete reliance on far-UV data. Adopting the 2σ upper limit on the M/L(z = 8), the stellar mass density to M UV,AB < −18 declines from ρ * (z = 7) = 3.7 +1.4 −1.8 ×10 6 M ⊙ Mpc −3 to ρ * (z = 8) < 8×10 5 M ⊙ Mpc −3 , following ∝ (1 + z) −6 over 3 < z < 8. Lower masses at z = 8 would signify more dramatic evolution, which can be established with deeper IRAC observations, long before the arrival of the James Webb Space Telescope.

The Astrophysical Journal, 2011

We derive stellar masses from SED fitting to rest-frame optical and UV fluxes for 401 star-formin... more We derive stellar masses from SED fitting to rest-frame optical and UV fluxes for 401 star-forming galaxies at z ∼ 4, 5, and 6 from Hubble-WFC3/IR observations of the ERS combined with the deep GOODS-S Spitzer/IRAC data (and include a previously-published z ∼ 7 sample). A massluminosity relation with strongly luminosity-dependent M/L UV ratios is found for the largest sample (299 galaxies) at z ∼ 4. The relation M ∝ L 1.7(±0.2) UV,1500 has a well-determined intrinsic sample variance of 0.5 dex. This relation is also consistent with the more limited samples at z ∼ 5 − 7. This z ∼ 4 mass-luminosity relation, and the well-established faint UV luminosity functions at z ∼ 4 − 7, are used to derive galaxy mass functions (MF) to masses M ∼ 10 8 at z ∼ 4 − 7. A bootstap approach is used to derive the MFs to account for the large scatter in the M-L UV relation and the luminosity function uncertainties, along with an analytical crosscheck. The MFs are also corrected for the effects of incompleteness. The incompleteness-corrected MFs are steeper than previously found, with slopes α M ∼ −1.4 to −1.6 at low masses. These slopes are, however, still substantially flatter than the MFs obtained from recent hydrodynamical simulations. We use these MFs to estimate the stellar mass density (SMD) of the universe to a fixed M UV,AB < −18 as a function of redshift and find a SMD growth ∝ (1+z) −3.4±0.8 from z ∼ 7 to z ∼ 4. We also derive the SMD from the completeness-corrected MFs to a mass limit M ∼ 10 8 M ⊙ . Such completeness-corrected MFs and the derived SMDs will be particularly important for model comparisons as future MFs reach to lower masses.

The Astrophysical Journal, 2013

The Astrophysical Journal Supplement Series, 2009

We present a new, K-selected, optical-to-near infrared photometric catalog of the Extended Chandr... more We present a new, K-selected, optical-to-near infrared photometric catalog of the Extended Chandra Deep Field South (ECDFS), making it publicly available to the astronomical community. 1 The dataset is founded on publicly available imaging, supplemented by original z ′ JK imaging data collected as part of the MUltiwavelength Survey by Yale-Chile (MUSYC). The final photometric catalog consists of photometry derived from U U 38 BV RIz ′ JK imaging covering the full 1 2 × 1 2 • of the ECDFS, plus H band photometry for approximately 80 % of the field. The 5σ flux limit for pointsources is K (AB) tot = 22.0. This is also the nominal completeness and reliability limit of the catalog: the empirical completeness for 21.75 < K < 22.00 is 85 %. We have verified the quality of the catalog through both internal consistency checks, and comparisons to other existing and publicly available catalogs. As well as the photometric catalog, we also present catalogs of photometric redshifts and restframe photometry derived from the ten band photometry. We have collected robust spectroscopic redshift determinations from published sources for 1966 galaxies in the catalog. Based on these sources, we have achieved a (1σ) photometric redshift accuracy of ∆z/(1 + z) = 0.036, with an outlier fraction of 7.8 %. Most of these outliers are X-ray sources. Finally, we describe and release a utility for interpolating restframe photometry from observed SEDs, dubbed InterRest 2 . Particularly in concert with the wealth of already publicly available data in the ECDFS, this new MUSYC catalog provides an excellent resource for studying the changing properties of the massive galaxy population at z 2.

Current observations of the most massive galaxies at 0&amp;amp;amp;amp;amp;amp;amp;amp;amp;am... more Current observations of the most massive galaxies at 0&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;lt;z&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;lt;1 suggest that they evolve very slowly, contrary to expectations from galaxy formation models. Unfortunately it has proven difficult to push these studies to higher redshifts, because broad-band near-infrared surveys do not have the required redshift accuracy. We have recently developed and implemented an extremely efficient technique to measure accurate redshifts of

Hildebrandt et al. (2006A&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp... more Hildebrandt et al. (2006A&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;A...452.1121H) have collected all (up until 2005 December) archival UU38BRVI imaging data taken using the Wide Field Imager (WFI) on the ESO MPG 2.2m telescope. We have supplemented the WFI optical data with original z&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;#39;-band imaging taken using Mosaic-II camera on the CTIO 4m Blanco telescope. The ECDFS data were taken in 2005 January. The new MUSYC

The Astrophysical Journal Supplement Series, 2015

ABSTRACT In this paper we present the MOSFIRE Deep Evolution Field (MOSDEF) survey. The MOSDEF su... more ABSTRACT In this paper we present the MOSFIRE Deep Evolution Field (MOSDEF) survey. The MOSDEF survey aims to obtain moderate-resolution (R=3000-3650) rest-frame optical spectra (~3700-7000 Angstrom) for ~1500 galaxies at 1.37&lt;z&lt;3.80 in three well-studied CANDELS fields: AEGIS, COSMOS, and GOODS-N. Targets are selected in three redshift intervals: 1.37&lt;z&lt;1.70, 2.09&lt;z&lt;2.61, and 2.95&lt;z&lt;3.80, down to fixed H_AB (F160W) magnitudes of 24.0, 24.5 and 25.0, respectively, using the photometric and spectroscopic catalogs from the 3D-HST survey. We target both strong nebular emission lines (e.g., [OII], Hbeta, [OIII], 5008, Halpha, [NII], and [SII]) and stellar continuum and absorption features (e.g., Balmer lines, Ca-II H and K, Mgb, 4000 Angstrom break). Here we present an overview of our survey, the observational strategy, the data reduction and analysis, and the sample characteristics based on spectra obtained during the first 24 nights. To date, we have completed 21 masks, obtaining spectra for 591 galaxies. For ~80% of the targets we identify and measure multiple emission or absorption lines. In addition, we confirm 55 additional galaxies, which were serendipitously detected. The MOSDEF galaxy sample includes unobscured star-forming, dusty star-forming, and quiescent galaxies and spans a wide range in stellar mass (~10^9-10^11.5 Msol) and star formation rate (~0-10^4 Msol/yr). The spectroscopically confirmed sample is roughly representative of an H-band limited galaxy sample at these redshifts. With its large sample size, broad diversity in galaxy properties, and wealth of available ancillary data, MOSDEF will transform our understanding of the stellar, gaseous, metal, dust, and black hole content of galaxies during the time when the universe was most active.