The Great Observatories Origins Deep Survey

The Great Observatories Origins Deep Survey (GOODS) is designed to gather the best and deepest multiwavelength data for studying the formation and evolution of galaxies and active galactic nuclei, the distribution of dark and luminous matter at high redshift, the cosmological parameters from distant supernovae, and the extragalactic background light. The program uses the most powerful space- and ground-based telescopes to cover two fields, each 10'x16', centered on the Hubble Deep Field North and the Chandra Deep Field South, already the sites of extensive observations from X-ray through radio wavelengths. GOODS incorporates 3.6-24 micron observations from a SIRTF Legacy Program, four-band ACS imaging from an HST Treasury Program, and extensive new ground-based imaging and spectroscopy. GOODS data products will be made available on a rapid time-scale, enabling community research on a wide variety of topics. Here we describe the project, emphasizing its application for studying the mass assembly history of galaxies.Comment: 8 pages, 2 figures, to appear in the proceedings of the ESO/USM Workshop "The Mass of Galaxies at Low and High Redshift" (Venice, Italy, October 2001), eds. R. Bender and A. Renzin

IRAC Deep Survey of COSMOS

Over the last four years, we have developed the COSMOS survey field with complete multi-wavelength coverage from radio to X-ray, including a total of 600 hours of Spitzer Legacy time (166 hours IRAC, 460 hours MIPS). Here we propose to deepen the IRAC 3.6 µm and 4.5 µm coverage with 3000 hours over 2.3 deg^2 area included in deep Subaru imaging. This extended mission deep survey will increase the sensitivity by a factor of 3–5. The most important impact will be that the COSMOS survey will then provide extremely sensitive photometric redshifts and stellar mass estimates for approximately a million galaxies out to z~6. We expect these data to detect approximately 1000 objects at z = 6 to 10. The data will also provide excellent temporal coverage for variability studies on timescales from days to the length of the extended mission

Probing Outflows in z= 1~2 Galaxies through FeII/FeII* Multiplets

We report on a study of the 2300-2600\AA FeII/FeII* multiplets in the rest-UV spectra of star-forming galaxies at 1.0<z<2.6 as probes of galactic-scale outflows. We extracted a mass-limited sample of 97 galaxies at z~1.0-2.6 from ultra-deep spectra obtained during the GMASS spetroscopic survey in the GOODS South field with the VLT and FORS2. We obtain robust measures of the rest equivalent width of the FeII absorption lines down to a limit of W_r>1.5 \AA and of the FeII* emission lines to W_r>0.5 \AA. Whenever we can measure the systemic redshift of the galaxies from the [OII] emission line, we find that both the FeII and MgII absorption lines are blueshifted, indicative that both species trace gaseous outflows. We also find, however, that the FeII gas has generally lower outflow velocity relative to that of MgII. We investigate the variation of FeII line profiles as a function of the radiative transfer properties of the lines, and find that transitions with higher oscillator strengths are more blueshifted in terms of both line centroids and line wings. We discuss the possibility that FeII lines are suppressed by stellar absorptions. The lower velocities of the FeII lines relative to the MgII doublet, as well as the absence of spatially extended FeII* emission in 2D stacked spectra, suggest that most clouds responsible for the FeII absorption lie close (3~4 kpc) to the disks of galaxies. We show that the FeII/FeII* multiplets offer unique probes of the kinematic structure of galactic outflows.Comment: 53 pages, 22 Figures, accepted for publication in ApJ, revised according to referee comment

Near-infrared emission line diagnostics for AGN from the local Universe to z ∼ 3*

Optical rest-frame spectroscopic diagnostics are usually employed to distinguish between star formation and active galactic nucleus (AGN) powered emission. However, this method is biased against dusty sources, hampering a complete census of the AGN population across cosmic epochs. To mitigate this effect, it is crucial to observe at longer wavelengths in the rest-frame near-infrared (near-IR), which is less affected by dust attenuation and can thus provide a better description of the intrinsic properties of galaxies. AGN diagnostics in this regime have not been fully exploited so far, due to the scarcity of near-IR observations of both AGN and star-forming galaxies, especially at redshifts higher than 0.5. Using Cloudy photoionization models, we identified new AGN – star formation diagnostics based on the ratio of bright near-IR emission lines, namely [SIII] 9530 Å, [CI] 9850 Å, [PII] 1.188 μm, [FeII] 1.257 μm, and [FeII] 1.64 μm to Paschen lines (either Paγ or Paβ), providing simple, analytical classification criteria. We applied these diagnostics to a sample of 64 star-forming galaxies and AGN at 0 ≤ z ≤ 1, and 65 sources at 1 ≤ z ≤ 3 recently observed with JWST-NIRSpec in CEERS. We find that the classification inferred from the near-IR is broadly consistent with the optical one based on the BPT and the [SII]/Hα ratio. However, in the near-IR, we find ∼60% more AGN than in the optical (13 instead of eight), with five sources classified as “hidden” AGN, showing a larger AGN contribution at longer wavelengths, possibly due to the presence of optically thick dust. The diagnostics we present provide a promising tool to find and characterize AGN from z = 0 to z ≃ 3 with low- and medium-resolution near-IR spectrographs in future surveys

Reconstructing the Assembly of Massive Galaxies. I: The Importance of the Progenitor Effect in the Observed Properties of Quiescent Galaxies at z≈2z\approx 2

We study the relationship between the morphology and star formation history (SFH) of 361 quiescent galaxies (QGs) at redshift $\langle z_{obs}\rangle\approx 2$, with stellar mass $\log M_*\ge10.3$, selected with the UVJ technique. Taking advantage of panchromatic photometry covering the rest-frame UV-to-NIR spectral range ($\approx40$ bands), we reconstruct the non-parametric SFH of the galaxies with the fully Bayesian SED fitting code Prospector. We find that the half-light radius $R_e$, observed at $z_{obs}$, depends on the formation redshift of the galaxies, $z_{form}$, and that this relationship depends on stellar mass. At $\log M_*<11$, the relationship is consistent with $R_e\propto(1+z_{form})^{-1}$, in line with the expectation that the galaxies' central density depends on the cosmic density at the time of their formation, i.e. the "progenitor effect". At $\log M_*>11$, the relationship between $R_e$ and $z_{form}$ flattens, suggesting that mergers become increasingly important for the size growth of more massive galaxies after they quenched. We also find that the relationship between $z_{form}$ and galaxy compactness similarly depends on stellar mass. While no clear trend is observed for QGs with $\log M_*>11$, lower-mass QGs that formed earlier, i.e. with larger $z_{form}$, have larger central stellar mass surface densities, both within the $R_e$ ($\Sigma_e$) and central 1 kpc ($\Sigma_{1kpc}$), and also larger $M_{1kpc}/M_*$, the fractional mass within the central 1 kpc. These trends between $z_{form}$ and compactness, however, essentially disappear, if the progenitor effect is removed by normalizing the stellar density with the cosmic density at $z_{form}$. Our findings highlight the importance of reconstructing the SFH of galaxies before attempting to infer their intrinsic structural evolution.Comment: 34 pages, 27 figures; Submitted to ApJ; Comments welcom

A Milky Way-like barred spiral galaxy at a redshift of 3

The majority of massive disk galaxies in the local Universe show a stellar barred structure in their central regions, including our Milky Way. Bars are supposed to develop in dynamically cold stellar disks at low redshift, as the strong gas turbulence typical of disk galaxies at high redshift suppresses or delays bar formation. Moreover, simulations predict bars to be almost absent beyond z = 1.5 in the progenitors of Milky Way-like galaxies. Here we report observations of ceers-2112, a barred spiral galaxy at redshift zphot ≈ 3, which was already mature when the Universe was only 2 Gyr old. The stellar mass (M★ = 3.9 × 109 M⊙) and barred morphology mean that ceers-2112 can be considered a progenitor of the Milky Way, in terms of both structure and massassembly history in the frst 2 Gyr of the Universe, and was the closest in mass in the frst 4 Gyr. We infer that baryons in galaxies could have already dominated over dark matter at z ≈ 3, that high-redshift bars could form in approximately 400 Myr and that dynamically cold stellar disks could have been in place by redshift z = 4–5 (more than 12 Gyrs ago)

The Stellar Masses and Star Formation Histories of Galaxies at z ≈ 6: Constraints from Spitzer Observations in the Great Observatories Origins Deep Survey

Using the deep Spitzer Infrared Array Camera (IRAC) observations of the Great Observatories Origins Deep Survey (GOODS), we study the stellar masses and star formation histories of galaxies at z approx 6 based on the i_(775)-band dropout sample selected from the GOODS fields. In total, we derive stellar masses for 53 i_(775)-band dropouts that have robust IRAC detections. These galaxies have typical stellar masses of ~10^(10) M_⊙ and typical ages of a couple of hundred million years, consistent with earlier results based on a smaller sample of z ≈ 6 galaxies. The existence of such massive galaxies at z ≈ 6 can be explained by at least one set of N-body simulations of the hierarchical paradigm. We also study 79 i_(775)-band dropouts that are invisible in the IRAC data and find that they are typically less massive by a factor of 10. These galaxies are much bluer than those detected by the IRAC, indicating that their luminosities are dominated by stellar populations with ages ≾ 40 Myr. Based on our mass estimates, we derive a lower limit to the global stellar mass density at z ≈ 6, which is 1.1-6.7 × 10^6 M_⊙ Mpc^(-3). The prospect of detecting the progenitors of the most massive galaxies at yet higher redshifts is explored. We also investigate the implication of our results for reionization and find that the progenitors of the galaxies comparable to those in our sample, even in the most optimized (probably unrealistic) scenario, cannot sustain the reionization for a period longer than ~2 Myr. Thus most of the photons required for reionization must have been provided by other sources, such as the progenitors of the dwarf galaxies that are far below our current detection capability

Steadily Increasing Star Formation Rates in Galaxies Observed at 3 <~ z <~ 5 in the CANDELS/GOODS-S Field

We investigate the star formation histories (SFHs) of high redshift (3 <~ z <~ 5) star-forming galaxies selected based on their rest-frame ultraviolet (UV) colors in the CANDELS/GOODS-S field. By comparing the results from the spectral-energy-distribution-fitting analysis with two different assumptions about the SFHs --- i.e., exponentially declining SFHs as well as increasing ones, we conclude that the SFHs of high-redshift star-forming galaxies increase with time rather than exponentially decline. We also examine the correlations between the star formation rates (SFRs) and the stellar masses. When the galaxies are fit with rising SFRs, we find that the trend seen in the data qualitatively matches the expectations from a semi-analytic model of galaxy formation. The mean specific SFR is shown to increase with redshift, also in agreement with the theoretical prediction. From the derived tight correlation between stellar masses and SFRs, we derive the mean SFH of star-forming galaxies in the redshift range of 3 <~ z <~ 5, which shows a steep power-law (with power alpha = 5.85) increase with time. We also investigate the formation timescales and the mean stellar population ages of these star-forming galaxies. Our analysis reveals that UV-selected star-forming galaxies have a broad range of the formation redshift. The derived stellar masses and the stellar population ages show positive correlation in a sense that more massive galaxies are on average older, but with significant scatter. This large scatter implies that the galaxies' mass is not the only factor which affects the growth or star formation of high-redshift galaxies.Comment: 31 pages, 8 figures, 2 table

Hubble Space Telescope Imaging of Star-Forming Galaxies at Redshifts z>3

We present HST images of star-forming galaxies at redshifts z>3. These galaxies have been color selected for having a Lyman discontinuity in the otherwise flat (in f_\nu units) UV spectra of unreddened star formation. The spectroscopic confirmation of these z>3 galaxies is reported in a companion paper (Steidel et al. 1996). The HST images probe the rest-frame UV at 1400--1900 Ang and show that the morphologies of the z>3 galaxies are generally compact, although we find a few cases of more diffuse light profiles and objects comprised of multiple compact structures. Overall, the dispersion of morphologies is relatively narrow, in contrast to the variety found in star-forming galaxies at intermediate redshifts (z~1). The galaxies with compact morphology are typically characterized by a small but resolved ``core'', approximately <0.7 arcsec in radius, or about 5 h_50 (8.5 h_50) kpc with q_0=0.5 (0.05), and half-light radii of 0.2--0.3 arcsec, or 1.4--2.1 h_50 (2.4--3.6 h_50) kpc. These sizes and scale lengths are similar to those of present-day bulges or intermediate-luminosity spheroids. The ``cores'' are often surrounded by lower surface-brightness nebulosities, generally asymmetrically distributed. The minority of more diffuse galaxies do not possess this core, and an exponential function provides a very good fit to their light profiles. In contrast to highly elongated or irregular structures, such as ``chain galaxies'', that are found at $z \sim 1$, the z>3 galaxies are characterized by a relatively high degree of spherical symmetry. Morphology, space density, star-formation rates, masses, and epoch of the star-formation phase all support the hypothesis that we have identified the progenitors of present-day luminous galaxies at the epoch when they were forming the stars ofComment: 15 pages; The Astrophysical Journa