The MOSDEF Survey: Broad Emission Lines at z=1.4-3.8
William R. Freeman, Brian Siana, Mariska Kriek, Alice E. Shapley, Naveen Reddy, Alison L. Coil, Bahram Mobasher, Alexander L. Muratov, Mojegan Azadi, Gene Leung… 展开作者
William R. Freeman, Brian Siana, Mariska Kriek, Alice E. Shapley, Naveen Reddy, Alison L. Coil, Bahram Mobasher, Alexander L. Muratov, Mojegan Azadi, Gene Leung, Ryan Sanders, Irene Shivaei, Sedona H. Price, Laura DeGroot, Dušan Kereš
We present results from the MOSFIRE Deep Evolution Field (MOSDEF) survey on broad flux from the nebular emission lines H$α$, [NII], [OIII], H$β$, and [SII]. The sample consists of 127 star-forming galaxies at $1.37 < z < 2.61$ and 84 galaxies at $2.95 < z < 3.80$. We decompose the emission lines using narrow ($\text{FWHM} < 275 \ \text{km s}^{-1}$) and broad ($\text{FWHM} > 300 \ \text{km s}^{-1}$) Gaussian components for individual galaxies and stacks. Broad emission is detected at $>3σ$ in $<10$% of galaxies and the broad flux accounts for 10-70% of the total flux. We find a slight increase in broad to narrow flux ratio with mass but note that we cannot reliably detect broad emission with $\text{FWHM} < 275 \ \text{km s}^{-1}$, which may be significant at low masses. Notably, there is a correlation between higher signal-to-noise (S/N) spectra and a broad component detection indicating a S/N dependence in our ability to detect broad flux. When placed on the N2-BPT diagram ([OIII]/H$β$ vs. [NII]/H$α$) the broad components of the stacks are shifted towards higher [OIII]/H$β$ and [NII]/$α$ ratios compared to the narrow component. We compare the location of the broad components to shock models and find that the broad component could be due to shocks, but we do not rule out other possibilities such as the presence of an AGN. We estimate the mass loading factor (mass outflow rate/star formation rate) assuming the broad component is a photoionized outflow and find that the mass loading factor increases as a function of mass which agrees with previous studies. We show that adding emission from shocked gas to $z\sim0$ SDSS spectra shifts galaxies towards the location of $z\sim2$ galaxies on several emission line diagnostic diagrams.
We analyze the completeness of the MOSDEF survey, in which z ~ 2 galaxies were selected for rest-optical spectroscopy from well-studied HST extragalactic legacy fields down to a fixed rest-optical magnitude limit (H_AB = 24.5). The subset of z ~ 2 MOSDEF galaxies with high signal-to-noise (S/N) emission-line detections analyzed in previous work represents a small minority (<10%) of possible z ~ 2 MOSDEF targets. It is therefore crucial to understand how representative this high S/N subsample is, while also more fully exploiting the MOSDEF spectroscopic sample. Using spectral-energy-distributio…
The combination of the MOSDEF and KBSS-MOSFIRE surveys represents the largest joint investment of Keck/MOSFIRE time to date, with ~3000 galaxies at 1.4<=z<=3.8, roughly half of which are at z~2. MOSDEF is photometric- and spectroscopic-redshift selected with a rest-optical magnitude limit, while KBSS-MOSFIRE is primarily selected based on rest-UV colors and a rest-UV magnitude limit. Analyzing both surveys in a uniform manner with consistent spectral-energy-distribution (SED) models, we find that the MOSDEF z~2 targeted sample has a higher median M_* and redder rest U-V color than the KBSS-MOS…
Using the MOSDEF rest-frame optical spectroscopic survey, we investigate the star-formation histories (SFHs) of different galaxy types, ranging from actively star forming to quiescent at $1.4\leq~z\leq2.6$. SFHs are constrained utilizing stellar continuum spectroscopy, specifically through a combination of Balmer absorption lines, the 4000$Å$ break, and the equivalent width of the H$α$ emission line. To attain a sufficiently high signal-to-noise ratio (S/N) to conduct these measurements we stack spectra of galaxies with similar spectral types, as determined from their rest-frame $U-V$ and $V-J…
Using observations from the first two years of the MOSFIRE Deep Evolution Field (MOSDEF) survey, we study 13 AGN-driven outflows detected from a sample of 67 X-ray, IR and/or optically-selected AGN at $z \sim 2$. The AGN have bolometric luminosities of $\sim10^{44}-10^{46} ~\mathrm{erg~s^{-1}}$, including both quasars and moderate-luminosity AGN. We detect blueshifted, ionized gas outflows in the H$β$ , [OIII], H$α$ ~and/or [NII] emission lines of $19\%$ of the AGN, while only 1.8\% of the MOSDEF galaxies have similarly-detected outflows. The outflow velocities span $\sim$300 to 1000 km s$^{-1…
We present results from the MOSFIRE Deep Evolution Field (MOSDEF) survey on rest-frame optical AGN identification and completeness at z~2.3. With our sample of 50 galaxies and 10 X-ray and IR-selected AGN with measured H-beta, [OIII], H-alpha, and [NII] emission lines, we investigate the location of AGN in the BPT, MEx (mass-excitation), and CEx (color-excitation) diagrams. We find that the BPT diagram works well to identify AGN at z~2.3 and that the z~0 AGN/star-forming galaxy classifications do not need to shift substantially at z~2.3 to robustly separate these populations. However, the MEx …
The observed empirical relation between the star-formation rates (SFR) of low-redshift galaxies and their radio continuum luminosity offers a potential means of measuring SFR in high redshift galaxies that is unaffected by dust obscuration. In this study, we make the first test for redshift evolution in the SFR-radio continuum relation at high redshift using dust-corrected H$α$ SFR. Our sample consists of 178 galaxies from the MOSFIRE Deep Evolution Field (MOSDEF) Survey at $1.4 < z < 2.6$ with rest-frame optical spectroscopy and deep 1.5 GHz radio continuum observations from the Karl G. Jansk…
We present results on the emission-line properties of 1.3<=z<=2.7 galaxies drawn from the complete MOSFIRE Deep Evolution Field (MOSDEF) survey. Specifically, we use observations of the emission-line diagnostic diagram of [OIII]5007/Hb vs. [SII]6717,6731/Ha, i.e., the "[SII] BPT diagram," to gain insight into the physical properties of high-redshift star-forming regions. High-redshift MOSDEF galaxies are offset towards lower [SII]6717,6731/Ha at fixed [OIII]5007/Hb, relative to local galaxies from the Sloan Digital Sky Survey (SDSS). Furthermore, at fixed [OIII]5007/Hb, local SDSS galaxies fol…
We study the properties of 55 morphologically-identified merging galaxy systems at z~2. These systems are flagged as mergers based on features such as tidal tails, double nuclei, and asymmetry. Our sample is drawn from the MOSFIRE Deep Evolution Field (MOSDEF) survey, along with a control sample of isolated galaxies at the same redshift. We consider the relationships between stellar mass, star formation rate (SFR), and gas-phase metallicity for both merging and non-merging systems. In the local universe, merging systems are characterized by an elevated SFR and depressed metallicity compared to…
We present results on the excitation properties of z~2.3 galaxies using early observations from the MOSFIRE Deep Evolution Field (MOSDEF) Survey. With its coverage of the full suite of strong rest-frame optical emission lines, MOSDEF provides an unprecedented view of the rest-frame optical spectra of a representative sample of distant star-forming galaxies. We investigate the locations of z~2.3 MOSDEF galaxies in multiple emission-line diagnostic diagrams. These include the [OIII]/Hb vs. [NII]/Ha and [OIII]/Hb vs. [SII]/Ha "BPT" diagrams, as well as the O_32 vs. R_23 excitation diagram. We rec…
We present results on the properties of neon emission in $z\sim2$ star-forming galaxies drawn from the MOSFIRE Deep Evolution Field (MOSDEF) survey. Doubly-ionized neon ([NeIII]3869) is detected at $\geq3σ$ in 61 galaxies, representing $\sim$25% of the MOSDEF sample with H$α$, H$β$, and [OIII]$5007$ detections at similar redshifts. We consider the neon emission-line properties of both individual galaxies with [NeIII]3869 detections and composite $z\sim2$ spectra binned by stellar mass. With no requirement of [NeIII]3869 detection, the latter provide a more representative picture of neon emissi…
Using data from the MOSFIRE Deep Evolution Field (MOSDEF) survey, we present a census of AGN-driven ionized outflows in a sample of 159 AGNs at $1.4 \le z \le 3.8$. The sample spans AGN bolometric luminosities of $10^{44-47} \mathrm{~erg~s}^{-1}$ and includes both quiescent and star-forming galaxies extending across three orders of magnitude in stellar mass. We identify and characterize outflows from the \hbeta, [OIII], \halpha ~and [NII] emission line spectra. We detect outflows in $17\%$ of the AGNs, seven times more often than in a mass-matched sample of inactive galaxies in MOSDEF. The out…
We present an analysis using the MOSFIRE Deep Evolution Field (MOSDEF) survey on the nature of "MIR-excess" galaxies, which have star formation rates (SFR) inferred from mid-infrared (MIR) data that is substantially elevated relative to that estimated from dust-corrected UV data. We use a sample of $\sim$200 galaxies and AGN at $1.40<z<2.61$ with 24 $μ$m detections (rest-frame 8$μ$m) from MIPS/\textit{Spitzer}. We find that the identification of MIR-excess galaxies strongly depends on the methodologies used to estimate IR luminosity ($\rm L_{IR}$) and to correct the UV light for dust attenuati…
We present results from the MOSFIRE Deep Evolution Field (MOSDEF) survey on the identification, selection biases, and host galaxy properties of 55 X-ray, IR and optically-selected active galactic nuclei (AGN) at $1.4 < z < 3.8$. We obtain rest-frame optical spectra of galaxies and AGN and use the BPT diagram to identify optical AGN. We examine the uniqueness and overlap of the AGN identified at different wavelengths. There is a strong bias against identifying AGN at any wavelength in low mass galaxies, and an additional bias against identifying IR AGN in the most massive galaxies. AGN hosts sp…
We perform an aperture-matched analysis of dust-corrected H$α$ and UV SFRs using 303 star-forming galaxies with spectroscopic redshifts $1.36<z_\text{spec}<2.66$ from the MOSFIRE Deep Evolution Field (MOSDEF) survey. By combining H$α$ and H$β$ emission line measurements with multi-waveband resolved CANDELS/3D-HST imaging, we directly compare dust-corrected H$α$ and UV SFRs, inferred assuming a fixed attenuation curve shape and constant SFHs, within the spectroscopic aperture. Previous studies have found that H$α$ and UV SFRs inferred with these assumptions generally agree for typical star-form…
We study the properties of 30 spectroscopically-identified pairs of galaxies observed during the peak epoch of star formation in the universe. These systems are drawn from the MOSFIRE Deep Evolution Field (MOSDEF) Survey at $1.4 \leq z \leq 3.8$, and are interpreted as early-stage galaxy mergers. Galaxy pairs in our sample are identified as two objects whose spectra were collected on the same Keck/MOSFIRE spectroscopic slit. Accordingly, all pairs in the sample have projected separations $R_{\rm proj}\leq 60$ kpc. The velocity separation for pairs was required to be $Δv \leq 500 \mbox{ km s}^{…
We investigate the relationship between dust attenuation and stellar mass ($M_*$) in star-forming galaxies over cosmic time. For this analysis, we compare measurements from the MOSFIRE Deep Evolution Field (MOSDEF) survey at $z\sim2.3$ and the Sloan Digital Sky Survey (SDSS) at $z\sim0$, augmenting the latter optical dataset with both UV Galaxy Evolution Explorer (GALEX) and mid-infrared Wide-field Infrared Survey Explorer (WISE) photometry from the GALEX-SDSS-WISE Catalog. We quantify dust attenuation using both spectroscopic measurements of H$α$ and H$β$ emission lines, and photometric measu…
We present results on the z~2.3 mass-metallicity relation (MZR) using early observations from the MOSFIRE Deep Evolution Field (MOSDEF) survey. We use an initial sample of 87 star-forming galaxies with spectroscopic coverage of Hβ, [OIII]λ5007, Hα, and [NII]λ6584 rest-frame optical emission lines, and estimate the gas-phase oxygen abundance based on the N2 and O3N2 strong-line indicators. We find a positive correlation between stellar mass and metallicity among individual z~2.3 galaxies using both the N2 and O3N2 indicators. We also measure the emission-line ratios and corresponding oxygen abu…
We analyze the rest-optical emission-line ratios of z~1.5 galaxies drawn from the MOSFIRE Deep Evolution Field (MOSDEF) survey. Using composite spectra we investigate the mass-metallicity relation (MZR) at z~1.5 and measure its evolution to z=0. When using gas-phase metallicities based on the N2 line ratio, we find that the MZR evolution from z~1.5 to z=0 depends on stellar mass, evolving by $Δ\rm log(\rm O/H)\sim0.25$ dex at $M_*<10^{9.75}M_{\odot}$ down to $Δ\rm log(\rm O/H)\sim0.05$ at $M_*>10^{10.5}M_{\odot}$. In contrast, the O3N2-based MZR shows a constant offset of $Δ\rm log(\rm O/H)\si…
We present a detailed study of a galaxy merger taking place at $z=1.89$ in the GOODS-S field. Here we analyze Keck/MOSFIRE spectroscopic observations from the MOSFIRE Deep Evolution Field (MOSDEF) survey along with multi-wavelength photometry assembled by the 3D-HST survey. The combined dataset is modeled to infer the past star-formation histories (SFHs) of both merging galaxies. They are found to be massive, with log$_{10}(M_{\ast}/M_{\odot}) > 11$, with a close mass ratio satisfying the typical major-merger definition. Additionally, in the context of delayed-$τ$ models, GOODS-S 43114 and GOO…
We use a sample of 532 star-forming galaxies at redshifts $z\sim 1.4-2.6$ with deep rest-frame optical spectra from the MOSFIRE Deep Evolution Field (MOSDEF) survey to place the first constraints on the nebular attenuation curve at high redshift. Based on the first five low-order Balmer emission lines detected in the composite spectra of these galaxies (${\rm Hα}$ through ${\rm Hε}$), we derive a nebular attenuation curve that is similar in shape to that of the Galactic extinction curve, suggesting that the dust covering fraction and absorption/scattering properties along the lines-of-sight to…
We analyze the rest-optical emission-line spectra of $z\sim2.3$ star-forming galaxies in the complete MOSFIRE Deep Evolution Field (MOSDEF) survey. In investigating the origin of the well-known offset between the sequences of high-redshift and local galaxies in the [O III]5008/H$β$ vs. [N II]6585/H$α$ ("[N II] BPT") diagram, we define two populations of $z\sim2.3$ MOSDEF galaxies. These include the "high" population that is offset towards higher [O III]5008/H$β$ and/or [N II]6585/H$α$ with respect to the local SDSS sequence and the "low" population that overlaps the SDSS sequence. These two gr…
We investigate the nature of the relation among stellar mass, star-formation rate, and gas-phase metallicity (the M$_*$-SFR-Z relation) at high redshifts using a sample of 260 star-forming galaxies at $z\sim2.3$ from the MOSDEF survey. We present an analysis of the high-redshift M$_*$-SFR-Z relation based on several emission-line ratios for the first time. We show that a M$_*$-SFR-Z relation clearly exists at $z\sim2.3$. The strength of this relation is similar to predictions from cosmological hydrodynamical simulations. By performing a direct comparison of stacks of $z\sim0$ and $z\sim2.3$ ga…
We investigate the conditions that facilitate galactic-scale outflows using a sample of 155 typical star-forming galaxies at $z$~2 drawn from the MOSFIRE Deep Evolution Field (MOSDEF) survey. The sample includes deep rest-frame UV spectroscopy from the Keck Low-Resolution Imaging Spectrometer (LRIS), which provides spectral coverage of several low-ionisation interstellar (LIS) metal absorption lines and Ly$α$ emission. Outflow velocities are calculated from the centroids of the LIS absorption and/or Ly$α$ emission, as well as the highest-velocity component of the outflow from the blue wings of…
Using observations from the MOSFIRE Deep Evolution Field (MOSDEF) survey, we investigate the physical conditions of star-forming regions in $z\sim2.3$ galaxies, specifically the electron density and ionization state. From measurements of the [O II]$λλ$3726,3729 and [S II]$λλ$6716,6731 doublets, we find a median electron density of $\sim250$ cm$^{-3}$ at $z\sim2.3$, an increase of an order of magnitude compared to measurements of galaxies at $z\sim0$. While $z\sim2.3$ galaxies are offset towards significantly higher O$_{32}$ values relative to local galaxies at fixed stellar mass, we find that …
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<z<3.80 in three well-studied CANDELS fields: AEGIS, COSMOS, and GOODS-N. Targets are selected in three redshift intervals: 1.37<z<1.70, 2.09<z<2.61, and 2.95<z<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, […
We derive the UV-optical stellar dust attenuation curve of galaxies at z=1.4-2.6 as a function of gas-phase metallicity. We use a sample of 218 star-forming galaxies, excluding those with very young or heavily obscured star formation, from the MOSFIRE Deep Evolution Field (MOSDEF) survey with H$α$, H$β$, and [NII]$λ6585$ spectroscopic measurements. We constrain the shape of the attenuation curve by comparing the average flux densities of galaxies sorted into bins of dust obscuration using Balmer decrements, i.e., H$α$-to-H$β$ luminosities. The average attenuation curve for the high-metallicity…
We use extensive spectroscopy from the MOSFIRE Deep Evolution Field (MOSDEF) survey to investigate the relationships between rest-frame optical emission line equivalent widths ($W$) and a number of galaxy and ISM characteristics for a sample of $1134$ star-forming galaxies at redshifts $1.4\lesssim z\lesssim 3.8$. We examine how the equivalent widths of [OII]$λλ3727, 3730$, H$β$, [OIII]$λλ4960, 5008$, [OIII]$+$H$β$, H$α$, and H$α$+[NII]$λλ6550, 6585$, depend on stellar mass, UV slope, age, star-formation rate (SFR) and specific SFR (sSFR), ionization parameter and excitation conditions (O32 an…
We present the first direct comparison between Balmer line and panchromatic SED-based SFRs for z~2 galaxies. For this comparison we used 17 star-forming galaxies selected from the MOSFIRE Deep Evolution Field (MOSDEF) survey, with $3σ$ detections for H$α$ and at least two IR bands (Spitzer/MIPS 24$μ$m and Herschel/PACS 100 and 160$μ$m, and in some cases Herschel/SPIRE 250, 350, and 500$μ$m). The galaxies have total IR (8-1000$μ$m) luminosities of $\sim10^{11.4}-10^{12.4}\,\textrm{L}_\odot$ and star-formation rates (SFRs) of $\sim30-250\,\textrm{M}_\odot\,\mathrm{yr^{-1}}$. We fit the UV-to-far…
We present results on the dust attenuation curve of z~2 galaxies using early observations from the MOSFIRE Deep Evolution Field (MOSDEF) survey. Our sample consists of 224 star-forming galaxies with nebular spectroscopic redshifts in the range z= 1.36-2.59 and high S/N measurements of, or upper limits on, the H-alpha and H-beta emission lines obtained with Keck/MOSFIRE. We construct composite SEDs of galaxies in bins of specific SFR and Balmer optical depth in order to directly constrain the dust attenuation curve from the UV through near-IR for typical star-forming galaxies at high redshift. …
We present the first spectroscopic measurement of multiple rest-frame optical emission lines at $z>4$. During the MOSFIRE Deep Evolution Field (MOSDEF) survey, we observed the galaxy GOODSN-17940 with the Keck I/MOSFIRE spectrograph. The K-band spectrum of GOODSN-17940 includes significant detections of the [OII]$λλ3726,3729$, [NeIII]$\lambda3869$, and H$γ$ emission lines and a tentative detection of H$δ$, indicating $z_{\rm{spec}}=4.4121$. GOODSN-17940 is an actively star-forming $z>4$ galaxy based on its K-band spectrum and broadband spectral energy distribution. A significant excess relativ…
We present results on the star-formation rate (SFR) versus stellar mass ($M_*$) relation (i.e., the "main sequence") among star-forming galaxies at 1.37$\leq$$z$$\leq$2.61 using the MOSFIRE Deep Evolution Field (MOSDEF) survey. Based on a sample of 261 galaxies with H$α$ and H$β$ spectroscopy, we have estimated robust dust-corrected instantaneous SFRs over a large range in $M_*$ ($\sim10^{9.5}-10^{11.5}M_\odot$). We find a correlation between log(SFR(H$α$)) and log($M_*$) with a slope of 0.65$\pm$0.08 (0.58$\pm$0.10) at 1.4<z<2.6 (2.1<z<2.6). We find that different assumptions for the dust cor…
We present detections of [OIII]$λ$4363 and direct-method metallicities for star-forming galaxies at $z=1.7-3.6$. We combine new measurements from the MOSFIRE Deep Evolution Field (MOSDEF) survey with literature sources to construct a sample of 18 galaxies with direct-method metallicities at $z>1$, spanning $7.5<1$2+log(O/H$)<8.2$ and log(M$_*$/M$_{\odot})=7-10$. We find that strong-line calibrations based on local analogs of high-redshift galaxies reliably reproduce the metallicity of the $z>1$ sample on average. We construct the first mass-metallicity relation at $z>1$ based purely on direct-…
We use the large spectroscopic data set of the MOSFIRE Deep Evolution Field survey to investigate the kinematics and energetics of ionised gas outflows. Using a sample of 598 star-forming galaxies at redshift 1.4 < $z$ < 3.8, we decompose $\rm{H}α$ and [OIII] emission lines into narrow and broad components, finding significant detections of broad components in 10% of the sample. The ionised outflow velocity from individual galaxies appears independent of galaxy properties, such as stellar mass, star-formation rate (SFR), and star-formation-rate surface density ($Σ_{\rm SFR}$). Adopting a simpl…
Using the near-IR spectroscopy of the MOSFIRE Deep Evolution Field (MOSDEF) survey, we investigate the role of local environment in the gas-phase metallicity of galaxies. The local environment measurements are derived from accurate and uniformly calculated photometric redshifts with well-calibrated probability distributions. Based on rest-frame optical emission lines, [NII]$\lambda6584$ and H$α$, we measure gas-phase oxygen abundance of 167 galaxies at $1.37\leq z\leq1.7$ and 303 galaxies at $2.09\leq z\leq2.61$, located in diverse environments. We find that at $z\sim1.5$, the average metallic…
We present results on the variation of 7.7 micron Polycyclic Aromatic Hydrocarbon (PAH) emission in galaxies spanning a wide range in metallicity at z ~ 2. For this analysis, we use rest-frame optical spectra of 476 galaxies at 1.37 < z < 2.61 from the MOSFIRE Deep Evolution Field (MOSDEF) survey to infer metallicities and ionization states. Spitzer/MIPS 24 micron and Herschel/PACS 100 and 160 micron observations are used to derive rest-frame 7.7 micron luminosities (L(7.7)) and total IR luminosities (L(IR)), respectively. We find significant trends between the ratio of L(7.7) to L(IR) (and to…
We use a sample of 350 star-forming galaxies at $1.25<z<2.66$ from the MOSFIRE Deep Evolution Field survey to demonstrate an improved Voronoi binning technique that we use to study the properties of resolved stellar populations in $z\sim2$ galaxies. Stellar population and dust maps are constructed from the high-resolution CANDELS/3D-HST multi-band imaging. Rather than constructing the layout of resolved elements (i.e., Voronoi bins) from the S/N distribution of the $H_{160}$-band alone, we introduce a modified Voronoi binning method that additionally incorporates the S/N distribution of severa…
We investigate the evolution of galaxy gas-phase metallicity (O/H) over the range $z=0-3.3$ using samples of $\sim300$ galaxies at $z\sim2.3$ and $\sim150$ galaxies at $z\sim3.3$ from the MOSDEF survey. This analysis crucially utilizes different metallicity calibrations at $z\sim0$ and $z>1$ to account for evolving ISM conditions. We find significant correlations between O/H and stellar mass ($M_*$) at $z\sim2.3$ and $z\sim3.3$. The low-mass power law slope of the mass-metallicity relation is remarkably invariant over $z=0-3.3$, such that $\textrm{O/H}\propto M_*^{0.30}$ at all redshifts in th…
We present measurements of the electron-temperature based oxygen abundance for a highly star-forming galaxy at z=3.08, COSMOS-1908. This is the highest redshift at which [OIII]$λ$4363 has been detected, and the first time that this line has been measured at z>2. We estimate an oxygen abundance of 12+log(O/H)$=8.00^{+0.13}_{-0.14}$. This galaxy is a low-mass ($10^{9.3}$ M$_{\odot}$), highly star-forming ($\sim50$ M$_{\odot}$ yr$^{-1}$) system that hosts a young stellar population ($\sim160$ Myr). We investigate the physical conditions of the ionized gas in COSMOS-1908 and find that this galaxy …
The complex structure of gas, metals, and dust in the interstellar and circumgalactic medium (ISM and CGM, respectively) in star-forming galaxies can be probed by Ly$α$ emission and absorption, low-ionization interstellar (LIS) metal absorption, and dust reddening E(B-V). We present a statistical analysis of the mutual correlations among Ly$α$ equivalent width (EW$_{Lyα}$), LIS equivalent width (EW$_{LIS}$), and E(B-V) in a sample of 157 star-forming galaxies at $z\sim2.3$. With measurements obtained from individual, deep rest-UV spectra and spectral-energy distribution (SED) modeling, we find…
We present constraints on the massive star and ionized gas properties for a sample of 62 star-forming galaxies at $z\sim2.3$. Using BPASS stellar population models, we fit the rest-UV spectra of galaxies in our sample to estimate age and stellar metallicity which, in turn, determine the ionizing spectrum. In addition to the median properties of well-defined subsets of our sample, we derive the ages and stellar metallicities for 30 high-SNR individual galaxies -- the largest sample of individual galaxies at high redshift with such measurements. Most galaxies in this high-SNR subsample have stel…
We combine spectroscopic measurements of H$α$ and H$β$ and UV continuum photometry for a sample of 673 galaxies from the MOSFIRE Deep Evolution Field survey to constrain hydrogen ionizing photon production efficiencies ($ξ_{\rm ion}$, xi_ion) at z=1.4-2.6. We find average log(xi_ion/[Hz erg$^{-1}$])=25.06 (25.34), assuming the Calzetti (SMC) curve for the UV dust correction and a scatter of 0.28 dex in xi_ion distribution. After accounting for observational uncertainties and variations in dust attenuation, we conclude that the remaining scatter in xi_ion is likely dominated by galaxy-to-galaxy…
Population synthesis models predict that high-mass X-ray binary (HMXB) populations produced in low metallicity environments should be more X-ray luminous, a trend supported by studies of nearby galaxies. This trend may be responsible for the observed increase of the X-ray luminosity ($L_{\mathrm{X}}$) per star formation rate (SFR) with redshift due to the decrease of metallicity ($Z$) at fixed stellar mass as a function of redshift. To test this hypothesis, we use a sample of 79 $z\sim2$ star-forming galaxies with oxygen abundance measurements from the MOSDEF survey, which obtained rest-frame …
We present measurements of [SIII]$λλ$9069,9531 for a sample of $z\sim1.5$ star-forming galaxies, the first sample with measurements of these lines at z>0.1. We employ the line ratio S$_{32}$$\equiv$[SIII]$λλ$9069,9531/[SII]$λλ$6716,6731 as a novel probe of evolving ISM conditions. Since this ratio includes the low-ionization line [SII], it is crucial that the effects of diffuse ionized gas (DIG) on emission-line ratios be accounted for in $z\sim0$ integrated galaxy spectra, or else that comparisons be made to samples of local HII regions in which DIG emission is not present. We find that S$_{3…
We define a new morphology metric called "patchiness" ($P$) that is sensitive to deviations from the average of a resolved distribution, does not require the galaxy center to be defined, and can be used on the spatially-resolved distribution of any galaxy property. While the patchiness metric has a broad range of applications, we demonstrate its utility by investigating the distribution of dust in the interstellar medium of 310 star-forming galaxies at spectroscopic redshifts $1.36<z<1.66$ observed by the MOSFIRE Deep Evolution Field (MOSDEF) survey. The stellar continuum reddening distributio…
We present a joint analysis of rest-UV and rest-optical spectra obtained using Keck/LRIS and Keck/MOSFIRE for a sample of 62 star-forming galaxies at $z\sim2.3$. We divide our sample into 2 bins based on their location in the [OIII]/Hb vs. [NII]/Ha BPT diagram, and perform the first differential study of the rest-UV properties of massive ionizing stars as a function of rest-optical emission-line ratios. Fitting BPASS stellar population synthesis models, including nebular continuum emission, to our rest-UV spectra, we find that high-redshift galaxies offset towards higher [OIII]/Hb and [NII]/Ha…
We present ionized gas kinematics for 681 galaxies at $z\sim 1.4-3.8$ from the MOSFIRE Deep Evolution Field survey, measured using models which account for random galaxy-slit misalignments together with structural parameters derived from CANDELS Hubble Space Telescope (HST) imaging. Kinematics and sizes are used to derive dynamical masses. Baryonic masses are estimated from stellar masses and inferred gas masses from dust-corrected star formation rates (SFRs) and the Kennicutt-Schmidt relation. We measure resolved rotation for 105 galaxies. For the remaining 576 galaxies we use models based on…
We present H$α$ gas kinematics for 178 star-forming galaxies at z~2 from the MOSFIRE Deep Evolution Field survey. We have developed models to interpret the kinematic measurements from fixed-angle multi-object spectroscopy, using structural parameters derived from CANDELS HST/F160W imaging. For 35 galaxies we measure resolved rotation with a median $(V/σ_{V,0})_{R_E}=2.1$. We derive dynamical masses from the kinematics and sizes and compare them to baryonic masses, with gas masses estimated from dust-corrected H$α$ star formation rates (SFRs) and the Kennicutt-Schmidt relation. When assuming th…
We simulate the emission line galaxy properties for the Nancy Grace Roman Space Telescope by creating a 4 deg$^{2}$ galaxy mock catalog using Galacticus, a semi-analytic model (SAM) for galaxy formation and evolution. The simulated galaxy properties include emission line luminosity, equivalent width (EW), broad band photometry, and spectral energy distribution (SED). We compare this mock catalog with the latest observational data from WISP and MOSDEF. We find that our Galacticus model makes predictions consistent with observational data, over a wide redshift range for multiple emission lines. …
The AURORA Survey: Multiple Balmer and Paschen Emission Lines for Individual Star-forming Galaxies at z=1.5-4.4. II. Implications for Nebular Dust Corrections, Nebular SFRs, and Differential Reddening
University of California, Riverside（加州大学河滨分校）；University of California, Los Angeles（加州大学洛杉矶分校）；University of California, Davis（加州大学戴维斯分校）；University of Arizona（亚利桑那大学）；Max-Planck-Institut für extraterrestrische Physik（马克斯·普朗克地外物理学研究所）；California Institute of Technology（加州理工学院）；University College London（伦敦大学学院）
Galaxies in the reionization-era have been shown to have prominent [OIII]+H$β$ emission. Little is known about the gas conditions and radiation field of this population, making it challenging to interpret the spectra emerging at $z\gtrsim6$. Motivated by this shortcoming, we have initiated a large MMT spectroscopic survey identifying rest-frame optical emission lines in 227 intense [OIII] emitting galaxies at $1.3<z<2.4$. This sample complements the MOSDEF and KBSS surveys, extending to much lower stellar masses ($10^7-10^8 M_\odot$) and larger specific star formation rates ($5-300$ Gyr$^{-1}$…
The Heterodyne Instrument for the Far Infrared (HIFI) aboard the Herschel Space Observatory has acquired high-resolution broadband molecular spectra of star-forming regions in a wavelength range that is mostly inaccessible from ground-based astronomical observatories. These spectral surveys provide new insight into the chemical composition and physical properties of molecular clouds. In this manuscript, we present initial results from the HIFI spectral survey of the Sagittarius B2(N) molecular cloud, which contains spectral features assigned to at least 40 different molecules in a range of phy…
Presented here are the results of a broadband spectral line survey of the Sgr B2(N) - LMH region from 260 - 286 GHz using the Caltech Submillimeter Observatory. The data were taken over the course of a single night (May 26, 2013) during the course of science testing of the remote observational capabilities of the facility. The data are freely available to public both as raw, double-side band observational data and as a minimally-reduced ascii spectrum. The procedural scripts used for the preliminary data reduction using CLASS are provided as well. The observational parameters and preliminary d…
This paper considers a very special set of a few interstellar features --- broad diffuse interstellar bands (DIBs) at 4430, 4882, 5450, 5779 and 6175 ÅÅ. The set is small, and measurements of equivalent widths of these DIBs are challenging because of severe stellar, interstellar, and sometimes, also telluric contaminations inside their broad profiles. Nevertheless, we demonstrate that they do correlate pretty tightly (DIBs 4882 and 5450 to a lesser extent though) with other narrower diffuse bands, as well as with the color excess E(B$-$V). The studied broad DIBs correlate well with both inters…
The Sloan Digital Sky Survey (SDSS) discovered a few unusual quasars with a characteristic break in the continuum around 3000 A that neither shows the typical structure of broad absorption line (BAL) troughs nor is explained by typical intrinsic dust reddening. We used the method of Kohonen self-organising maps for a systematical search for quasars with such properties in the SDSS spectra archive. We constructed a sample of 23 quasars classified as 3000 A break quasars and two comparison samples of quasars with similar properties, to some extent, but also showing typical BAL features. We compu…
