James W. Colbert

The First Release COSMOS Optical and Near-IR Data and Catalog*

We present imaging data and photometry for the COSMOS survey in 15 photometric bands between 0.3 and 2.4 μm. These include data taken on the Subaru 8.3 m telescope, the KPNO and CTIO 4 m telescopes, and the CFHT 3.6 m telescope. Special techniques are used to ensure that the relative photometric calibration is better than 1% across the field of view. The absolute photometric accuracy from standard-star measurements is found to be 6%. The absolute calibration is corrected using galaxy spectra, providing colors accurate to 2% or better. Stellar and galaxy colors and counts agree well with the expected values. Finally, as the first step in the scientific analysis of these data we construct panchromatic number counts which confirm that both the geometry of the universe and the galaxy population are evolving.

VERY STRONG EMISSION-LINE GALAXIES IN THE WFC3 INFRARED SPECTROSCOPIC PARALLEL SURVEY AND IMPLICATIONS FOR HIGH-REDSHIFT GALAXIES* , **

The WFC3 Infrared Spectroscopic Parallel Survey uses the Hubble Space Telescope (HST) infrared grism capabilities to obtain slitless spectra of thousands of galaxies over a wide redshift range including the peak of star formation history of the universe. We select a population of very strong emission-line galaxies with rest-frame equivalent widths (EWs) higher than 200 A. A total of 176 objects are found over the redshift range 0.35 < z < 2.3 in the 180 arcmin^2 area that we have analyzed so far. This population consists of young and low-mass starbursts with high specific star formation rates (sSFR). After spectroscopic follow-up of one of these galaxies with Keck/Low Resolution Imaging Spectrometer, we report the detection at z = 0.7 of an extremely metal-poor galaxy with 12 + log(O/H) =7.47 ± 0.11. After estimating the active galactic nucleus fraction in the sample, we show that the high-EW galaxies have higher sSFR than normal star-forming galaxies at any redshift. We find that the nebular emission lines can substantially affect the total broadband flux density with a median brightening of 0.3 mag, with some examples of line contamination producing brightening of up to 1 mag. We show that the presence of strong emission lines in low-z galaxies can mimic the color-selection criteria used in the z ~ 8 dropout surveys. In order to effectively remove low-redshift interlopers, deep optical imaging is needed, at least 1 mag deeper than the bands in which the objects are detected. Without deep optical data, most of the interlopers cannot be ruled out in the wide shallow HST imaging surveys. Finally, we empirically demonstrate that strong nebular lines can lead to an overestimation of the mass and the age of galaxies derived from fitting of their spectral energy distribution (SED). Without removing emission lines, the age and the stellar mass estimates are overestimated by a factor of 2 on average and up to a factor of 10 for the high-EW galaxies. Therefore, the contribution of emission lines should be systematically taken into account in SED fitting of star-forming galaxies at all redshifts.

MASSIVE GALAXIES IN COSMOS: EVOLUTION OF BLACK HOLE VERSUS BULGE MASS BUT NOT VERSUS TOTAL STELLAR MASS OVER THE LAST 9 Gyr?*

We constrain the ratio of black hole (BH) mass to total stellar mass of type-1 active galactic nuclei (AGNs) in the COSMOS survey at 1 < z < 2. For 10 AGNs at mean redshift z ~ 1.4 with both Hubble Space Telescope (HST)/ACS and HST/NICMOS imaging data, we are able to compute the total stellar mass M_(*,total), based on rest-frame UV-to-optical host galaxy colors which constrain mass-to-light ratios. All objects have virial M_(BH) estimates available from the COSMOS Magellan/IMACS and zCOSMOS surveys. We find within errors zero difference between the M_(BH)-M_(*,total) relation at z ~ 1.4 and the M_(BH)-M_(*,bulge) relation in the local universe. Our interpretation is (1) if our objects were purely bulge-dominated, the M_(BH)-M_(*,bulge) relation has not evolved since z ~ 1.4. However, (2) since we have evidence for substantial disk components, the bulges of massive galaxies (M_(*,total) = 11.1 ± 0.3 or log M_(BH) ~ 8.3 ± 0.2) must have grown over the last 9 Gyr predominantly by redistribution of the disk into the bulge mass. Since all necessary stellar mass exists in galaxies at z = 1.4, no star formation or addition of external stellar material is required, but only a redistribution, e.g., induced by minor and major merging or through disk instabilities. Merging, in addition to redistributing mass in the galaxy, will add both BH and stellar/bulge mass, but does not change the overall final M_(BH)/M_(*,bulge) ratio. Since the overall cosmic stellar and BH mass buildup trace each other tightly over time, our scenario of bulge formation in massive galaxies is independent of any strong BH feedback and means that the mechanism coupling BH and bulge mass until the present is very indirect.

DUST EXTINCTION FROM BALMER DECREMENTS OF STAR-FORMING GALAXIES AT 0.75 z 1.5 WITH HUBBLE SPACE TELESCOPE/WIDE-FIELD-CAMERA 3 SPECTROSCOPY FROM THE WFC3 INFRARED SPECTROSCOPIC PARALLEL SURVEY

Spectroscopic observations of H and H emission lines of 128 star-forming galaxies in the redshift range 0:75 z 1:5 are presented. These data were taken with slitless spectroscopy using the G102 and G141 grisms of the Wide-Field-Camera 3 (WFC3) on board the Hubble Space Telescope as part of the WFC3 Infrared Spectroscopic Parallel (WISP) survey. Interstellar dust extinction is measured from stacked spectra that cover the Balmer decrement (H /H ). We present dust extinction as a function of H luminosity (down to 3 10 41 erg s 1 ), galaxy stellar mass (reaching 4 10 8 M ), and rest-frame H equivalent width. The faintest galaxies are two times fainter in H luminosity than galaxies previously studied at z 1:5. An evolution is observed where galaxies of the same H luminosity have lower extinction at higher redshifts, whereas no evolution is found within our error bars with stellar mass. The lower H luminosity galaxies in our sample are found to be consistent with no dust extinction. We

Physical properties of emission-line galaxies at z ∼ 2 from near-infrared spectroscopy with magellan fire

We present results from near-infrared spectroscopy of 26 emission-line galaxies at z ~ 2.2 and z ~ 1.5 obtained with the Folded-port InfraRed Echellette (FIRE) spectrometer on the 6.5 m Magellan Baade telescope. The sample was selected from the WFC3 Infrared Spectroscopic Parallels survey, which uses the near-infrared grism of the Hubble Space Telescope Wide Field Camera 3 (WFC3) to detect emission-line galaxies over 0.3 ≾z ≾2.3. Our FIRE follow-up spectroscopy (R ~ 5000) over 1.0-2.5 μm permits detailed measurements of the physical properties of the z ~ 2 emission-line galaxies. Dust-corrected star formation rates for the sample range from ~5-100 M☉ yr^(–1) with a mean of 29 M☉ yr^(–1). We derive a median metallicity for the sample of 12 + log(O/H) = 8.34 or ~0.45 Z☉. The estimated stellar masses range from ~10^(8.5)-10^(9.5) M☉, and a clear positive correlation between metallicity and stellar mass is observed. The average ionization parameter measured for the sample, log U ≈–2.5, is significantly higher than what is found for most star-forming galaxies in the local universe, but similar to the values found for other star-forming galaxies at high redshift. We derive composite spectra from the FIRE sample, from which we measure typical nebular electron densities of ~100-400 cm^(–3). Based on the location of the galaxies and composite spectra on diagnostic diagrams, we do not find evidence for significant active galactic nucleus activity in the sample. Most of the galaxies, as well as the composites, are offset diagram toward higher [O III]/Hβ at a given [N II]/Hα, in agreement with other observations of z ≳1 star-forming galaxies, but composite spectra derived from the sample do not show an appreciable offset from the local star-forming sequence on the [O III]/Hβ versus [S II]/Hα diagram. We infer a high nitrogen-to-oxygen abundance ratio from the composite spectrum, which may contribute to the offset of the high-redshift galaxies from the local star-forming sequence in the [O III]/Hβ versus [N II]/Hα diagram. We speculate that the elevated nitrogen abundance could result from substantial numbers of Wolf-Rayet stars in starbursting galaxies at z ~ 2.

ISO LWS spectroscopy of M82: A unified evolutionary model

We present the first complete far-infrared spectrum (43-197 μm) of M82, the brightest infrared galaxy in the sky, taken with the Long Wavelength Spectrometer of the Infrared Space Observatory (ISO). We detected seven fine structure emission lines, [O I] 63 and 145 μm, [O III] 52 and 88 μm , [N II] 122 μm, [N III] 57 μm, and [C II] 158 μm, and fitted their ratios to a combination starburst and photodissociation region (PDR) model. The best fit is obtained with H II regions with n = 250 cm-3, an ionization parameter of 10-3.5, and PDRs with n = 103.3 cm-3 and a far-ultraviolet flux of G0 = 102.8. We applied both continuous and instantaneous starburst models, with our best fit being a 3-5 Myr old instantaneous burst model with a 100 M⊙ cutoff. We also detected the ground-state rotational line of OH in absorption at 119.4 μm. No excited level OH transitions are apparent, indicating that the OH is almost entirely in its ground state with a column density ∼4 × 1014 cm-2. The spectral energy distribution over the long-wavelength spectrometer wavelength range is well fitted with a 48 K dust temperature and an optical depth, τDust ∝ λ-1.

THE WFC3 INFRARED SPECTROSCOPIC PARALLEL (WISP) SURVEY

We present the WFC3 Infrared Spectroscopic Parallel (WISP) Survey. WISP is obtaining slitless, near-infrared grism spectroscopy of ~90 independent, high-latitude fields by observing in the pure-parallel mode with the Wide Field Camera Three on the Hubble Space Telescope for a total of ~250 orbits. Spectra are obtained with the G_(102) (λ = 0.8–1.17 μm, R ~ 210) and G_(141) grisms (λ = 1.11–1.67 μm, R ~ 130), together with direct imaging in the J and H bands (F110W and F140W, respectively). In the present paper, we present the first results from 19 WISP fields, covering approximately 63 arcmin^2. For typical exposure times (~6400 s in G_(102) and ~2700 s in G_(141)), we reach 5σ detection limits for emission lines of f ~ 5 × 10^(−17) erg s^(−1) cm^(−2) for compact objects. Typical direct imaging 5σ limits are 26.3 and 26.1 mag. (AB) in F110W and F140W, respectively. Restricting ourselves to the lines measured with the highest confidence, we present a list of 328 emission lines, in 229 objects, in a redshift range 0.3 < z < 3. The single-line emitters are likely to be a mix of Hα and [O_III]5007,4959 A, with Hα predominating. The overall surface density of high-confidence emission-line objects in our sample is approximately 4 per arcmin^2. These first fields show high equivalent width sources, active galactic nucleus, and post-starburst galaxies. The median observed star formation rate (SFR) of our Hα-selected sample is 4M_⊙ yr^(−1). At intermediate redshifts, we detect emission lines in galaxies as faint as H_(140) ~ 25, or M_R < −19, and are sensitive to SFRs down to less than 1M_⊙ yr^(−1). The slitless grisms on WFC3 provide a unique opportunity to study the spectral properties of galaxies much fainter than L^* at the peak of the galaxy assembly epoch.

The Optical and Near-Infrared Morphologies of Isolated Early Type Galaxies

To study early-type galaxies in their simplest environments, we have constructed a well-defined sample of 30 isolated galaxies. The sample contains all early-type galaxies listed in the Third Reference Catalogue of Bright Galaxies (RC3) with no other cataloged galaxy with a known redshift lying within a projected radius of 1 h Mpc and ±1000 km s-1 (where we use the recession velocities in the RC3). We have obtained optical and near-infrared images of 23 of the galaxies and of a comparison sample of 13 early-type galaxies in X-ray–detected poor groups of galaxies. We have applied the techniques of unsharp-masking, galaxy model division, and color maps to search for morphological features that might provide clues to the evolution of these galaxies. Evidence for dust features is found in approximately 75% of both the isolated and group galaxies (17 of 22 and 9 of 12, respectively). However, shells or tidal features are much more prevalent in our isolated sample than in our group sample (9 of 22 = 41% vs. 1 of 12 = 8%, respectively). The isolation and colors of these shell galaxies make it unlikely that tidal interactions or asymmetric star formation are the causes of such features. One model that is not ruled out is that mergers produce the shells. If shells and dust are both merger signatures, the absence of shells in group elliptical galaxies implies that shells (1) form more easily, (2) are younger, and/or (3) are longer lived in isolated environments.

Spitzer Observations of the z = 2.73 Lensed Lyman Break Galaxy: MS 1512–cB58

We present Spitzer infrared (IR) photometry and spectroscopy of the lensed Lyman break galaxy (LBG) MS 1512–cB58 at z = 2.73. The large (factor ~30) magnification allows for the most detailed IR study of an L☉_(UV)(z = 3) LBG to date. Broadband photometry with IRAC (3-10 μm), IRS (16 μm), and MIPS (24, 70, and 160 μm) was obtained, as well as IRS spectroscopy spanning 5.5-35 μm. A fit of stellar population models to the optical/near-IR/IRAC photometry gives a young age (~9 Myr), forming stars at ~98 M⊙ yr^(-1), with a total stellar mass of ~10^9 M☉ formed thus far. The existence of an old stellar population with twice the stellar mass cannot be ruled out. IR spectral energy distribution fits to the 24 and 70 μm photometry, as well as previously obtained submillimeter/millimeter data give an intrinsic IR luminosity L_(IR) = (1–2) × 10^(11) L☉ and a star formation rate (SFR) ~20-40 M☉yr^(−1). The ultraviolet (UV) derived SFR is ~3-5 times higher than the SFR determined using L_(IR) or L_(Hα) because the red UV spectral slope is significantly overpredicting the level of dust extinction. This may suggest that the assumed Calzetti starburst obscuration law is not valid in young LBGs. We detect strong line emission from polycyclic aromatic hyrdrocarbons (PAHs) at 6.2, 7.7, and 8.6 μm. The line ratios are consistent with ratios observed in both local and high-redshift starbursts. Both the PAH and rest-frame 8 μm luminosities predict the total LIR based on previously measured relations in starbursts. Finally, we do not detect the 3.3 μm PAH feature. This is marginally inconsistent with some PAH emission models, but still consistent with PAH ratios measured in many local star-forming galaxies.

LOW MASSES AND HIGH REDSHIFTS: THE EVOLUTION OF THE MASS-METALLICITY RELATION*

We present the first robust measurement of the high redshift mass-metallicity (MZ) relation at 10^8 ≾ M/M_☉ ≾ 10^(10), obtained by stacking spectra of 83 emission-line galaxies with secure redshifts between 1.3 ≾ z ≾ 2.3. For these redshifts, infrared grism spectroscopy with the Hubble Space Telescope Wide Field Camera 3 is sensitive to the R_(23) metallicity diagnostic: ([O II] λλ3726, 3729 + [O III] λλ4959, 5007)/Hβ. Using spectra stacked in four mass quartiles, we find a MZ relation that declines significantly with decreasing mass, extending from 12+log(O/H) = 8.8 at M = 10^(9.8) M_☉, to 12+log(O/H) = 8.2 at M = 10^(8.2) M_☉. After correcting for systematic offsets between metallicity indicators, we compare our MZ relation to measurements from the stacked spectra of galaxies with M ≳ 10^(9.5) M_☉ and z ~ 2.3. Within the statistical uncertainties, our MZ relation agrees with the z ~ 2.3 result, particularly since our somewhat higher metallicities (by around 0.1 dex) are qualitatively consistent with the lower mean redshift (z = 1.76) of our sample. For the masses probed by our data, the MZ relation shows a steep slope which is suggestive of feedback from energy-driven winds, and a cosmological downsizing evolution where high mass galaxies reach the local MZ relation at earlier times. In addition, we show that our sample falls on an extrapolation of the star-forming main sequence (the SFR-M_* relation) at this redshift. This result indicates that grism emission-line selected samples do not have preferentially high star formation rates (SFRs). Finally, we report no evidence for evolution of the mass-metallicity-SFR plane; our stack-averaged measurements show excellent agreement with the local relation.