29 research outputs found
An Updated Dust-to-Star Geometry: Dust Attenuation Does Not Depend on Inclination in Star-Forming Galaxies from MOSDEF
We investigate dust attenuation and its dependence on viewing angle for 308
star-forming galaxies at from the MOSFIRE Deep Evolution
Field (MOSDEF) survey. We divide galaxies with a detected H emission
line and coverage of H into eight groups by stellar mass, star formation
rate (SFR), and inclination (i.e., axis ratio), then stack their spectra. From
each stack, we measure Balmer decrement and gas-phase metallicity, then we
compute median \AV and UV continuum spectral slope (). First, we find
that none of the dust properties (Balmer decrement, \AV, ) vary with
axis ratio. Second, both stellar and nebular attenuation increase with
increasing galaxy mass, showing little residual dependence on SFR or
metallicity. Third, nebular emission is more attenuated than stellar emission,
and this difference grows even larger at higher galaxy masses and SFRs. Based
on these results, we propose a three-component dust model where attenuation
predominantly occurs in star-forming regions and large, dusty star-forming
clumps, with minimal attenuation in the diffuse ISM. In this model, nebular
attenuation primarily originates in clumps, while stellar attenuation is
dominated by star-forming regions. Clumps become larger and more common with
increasing galaxy mass, creating the above mass trends. Finally, we argue that
a fixed metal yield naturally leads to mass regulating dust attenuation. Infall
of low-metallicity gas increases SFR and lowers metallicity, but leaves dust
column density mostly unchanged. We quantify this idea using the
Kennicutt-Schmidt and fundamental metallicity relations, showing that galaxy
mass is indeed the primary driver of dust attenuation.Comment: 19 pages, 13 figures, accepted for publication in Ap
The MOSDEF Survey: Untangling the Emission-line Properties of z ∼ 2.3 Star-forming Galaxies
We analyze the rest-optical emission-line spectra of z∼2.3 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/Hβ vs. [N II]6585/Hα ("[N II] BPT") diagram, we define two populations of z∼2.3 MOSDEF galaxies. These include the "high" population that is offset towards higher [O III]5008/Hβ and/or [N II]6585/Hα with respect to the local SDSS sequence and the "low" population that overlaps the SDSS sequence. These two groups are also segregated within the [O III]5008/Hβ vs. [S II]6718,6733/Hα and the [O III]4960,5008/[O II]3727,3730 (O32) vs. ([O III]4960,5008+[O II]3727,3730)/Hβ (R23) diagram, which suggests qualitatively that star-forming regions in the more offset galaxies are characterized by harder ionizing spectra at fixed nebular oxygen abundance. We also investigate many galaxy properties of the split sample and find that the "high" sample is on average smaller in size and less massive, but has higher specific star-formation rate and star-formation-rate surface density values and is slightly younger compared to the "low" population. From Cloudy+BPASS photoionization models, we estimate that the "high" population has a lower stellar metallicity (i.e., harder ionizing spectrum) but slightly higher nebular metallicity and higher ionization parameter compared to the "low" population. While the "high" population is more α-enhanced (i.e., higher α/Fe) than the "low" population, both samples are significantly more α-enhanced compared to local star-forming galaxies with similar rest-optical line ratios. These differences must be accounted for in all high-redshift star-forming galaxies -- not only those "offset" from local excitation sequences
The MOSDEF Survey: Neon as a Probe of ISM Physical Conditions at High Redshift
We present results on the properties of neon emission in
star-forming galaxies drawn from the MOSFIRE Deep Evolution Field (MOSDEF)
survey. Doubly-ionized neon ([NeIII]3869) is detected at in 61
galaxies, representing 25% of the MOSDEF sample with H, H,
and [OIII] detections at similar redshifts. We consider the neon
emission-line properties of both individual galaxies with [NeIII]3869
detections and composite spectra binned by stellar mass. With no
requirement of [NeIII]3869 detection, the latter provide a more representative
picture of neon emission-line properties in the MOSDEF sample. The
[NeIII]3869/[OII]3727 ratio (Ne3O2) is anti-correlated with stellar mass in
galaxies, as expected based on the mass-metallicity relation. It is
also positively correlated with the [OIII]/[OII] ratio (O32), but
line ratios are offset towards higher Ne3O2 at fixed O32, compared
with both local star-forming galaxies and individual H~II regions. Despite the
offset towards higher Ne3O2 at fixed O32 at , biases in inferred
Ne3O2-based metallicity are small. Accordingly, Ne3O2 may serve as an important
metallicity indicator deep into the reionization epoch. Analyzing additional
rest-optical line ratios including [NeIII]/[OIII] (Ne3O3) and
[OIII]/H (O3H), we conclude that the nebular emission-line
ratios of star-forming galaxies suggest a harder ionizing spectrum
(lower stellar metallicity, i.e., Fe/H) at fixed gas-phase oxygen abundance,
compared to systems at . These new results based on neon lend support
to the physical picture painted by oxygen, nitrogen, hydrogen, and sulfur
emission, of an ionized ISM in high-redshift star-forming galaxies irradiated
by chemically young, -enhanced massive stars.Comment: 7 pages, 5 figures, accepted to ApJ Letter
What Does the Geometry of the HβBLR Depend On?
We combine our dynamical modeling black-hole mass measurements from the Lick AGN Monitoring Project 2016 sample with measured cross-correlation time lags and line widths to recover individual scale factors, f, used in traditional reverberation-mapping analyses. We extend our sample by including prior results from Code for AGN Reverberation and Modeling of Emission Lines (CARAMEL) studies that have utilized our methods. Aiming to improve the precision of black-hole mass estimates, as well as uncover any regularities in the behavior of the broad-line region (BLR), we search for correlations between f and other AGN/BLR parameters. We find (i) evidence for a correlation between the virial coefficient log10(fmean,σ) and black-hole mass, (ii) marginal evidence for a similar correlation between log10( frms,σ) and black-hole mass, (iii) marginal evidence for an anticorrelation of BLR disk thickness with log10( fmean,FWHM) and log10( frms,FWHM), and (iv) marginal evidence for an anticorrelation of inclination angle with log10( fmean,FWHM), log10( frms,σ), and log10( fmean,σ). Last, we find marginal evidence for a correlation between line-profile shape, when using the root-mean-square spectrum, log10(FWHM/σ)rms, and the virial coefficient, log10( frms,σ), and investigate how BLR properties might be related to line-profile shape using CARAMEL models
The Lick AGN Monitoring Project 2016 : dynamical modeling of velocity-resolved Hβ lags in luminous Seyfert galaxies
K.H. acknowledges support from STFC grant ST/R000824/1.We have modeled the velocity-resolved reverberation response of the Hβ broad emission line in nine Seyfert 1 galaxies from the Lick Active Galactic Nucleus (AGN) Monitoring Project 2016 sample, drawing inferences on the geometry and structure of the low-ionization broad-line region (BLR) and the mass of the central supermassive black hole. Overall, we find that the Hβ BLR is generally a thick disk viewed at low to moderate inclination angles. We combine our sample with prior studies and investigate line-profile shape dependence, such as log10(FWHM/σ), on BLR structure and kinematics and search for any BLR luminosity-dependent trends. We find marginal evidence for an anticorrelation between the profile shape of the broad Hβ emission line and the Eddington ratio, when using the rms spectrum. However, we do not find any luminosity-dependent trends, and conclude that AGNs have diverse BLR structure and kinematics, consistent with the hypothesis of transient AGN/BLR conditions rather than systematic trends.Publisher PDFPeer reviewe
The Lick AGN Monitoring Project 2016: Dynamical Modeling of Velocity-Resolved H\b{eta} Lags in Luminous Seyfert Galaxies
We have modeled the velocity-resolved reverberation response of the H\b{eta}
broad emission line in nine Seyfert 1 galaxies from the Lick Active Galactic
Nucleus (AGN) Monitioring Project 2016 sample, drawing inferences on the
geometry and structure of the low-ionization broad-line region (BLR) and the
mass of the central supermassive black hole. Overall, we find that the H\b{eta}
BLR is generally a thick disk viewed at low to moderate inclination angles. We
combine our sample with prior studies and investigate line-profile shape
dependence, such as log10(FWHM/{\sigma}), on BLR structure and kinematics and
search for any BLR luminosity-dependent trends. We find marginal evidence for
an anticorrelation between the profile shape of the broad H\b{eta} emission
line and the Eddington ratio, when using the root-mean-square spectrum.
However, we do not find any luminosity-dependent trends, and conclude that AGNs
have diverse BLR structure and kinematics, consistent with the hypothesis of
transient AGN/BLR conditions rather than systematic trends
The Lick AGN Monitoring Project 2016 : velocity-resolved Hβ lags in luminous Seyfert galaxies
Funding: K.H. acknowledges support from STFC grant ST/R000824/1.We carried out spectroscopic monitoring of 21 low-redshift Seyfert 1 galaxies using the Kast double spectrograph on the 3 m Shane telescope at Lick Observatory from April 2016 to May 2017. Targetingactive galactic nuclei (AGN) with luminosities of λLλ(5100 Å) ≈ 1044 erg s−1 and predicted Hβ lags of∼ 20–30 days or black hole masses of 107–108.5 M⊙, our campaign probes luminosity-dependent trends in broad-line region (BLR) structure and dynamics as well as to improve calibrations for single-epoch estimates of quasar black hole masses. Here we present the first results from the campaign, including Hβ emission-line light curves, integrated Hβ lag times (8–30 days) measured against V -band continuum light curves, velocity-resolved reverberation lags, line widths of the broad Hβ components, and virial black hole mass estimates (107.1–108.1 M⊙). Our results add significantly to the number of existing velocity-resolved lag measurements and reveal a diversity of BLR gas kinematics at moderately high AGN luminosities. AGN continuum luminosity appears not to be correlated with the type of kinematics that its BLR gas may exhibit. Follow-up direct modeling of this dataset will elucidate the detailed kinematics and provide robust dynamical black hole masses for several objects in this sample.Publisher PDFPeer reviewe