Abstract
The Mapping Nearby Galaxies at Apache Point Observatory (MaNGA) Stellar Library (MaStar) is a large collection of high-quality empirical stellar spectra designed to cover all spectral types ...and ideal for use in the stellar population analysis of galaxies observed in the MaNGA survey. The library contains 59,266 spectra of 24,130 unique stars with spectral resolution
R
∼ 1800 and covering a wavelength range of 3622–10,354 Å. In this work, we derive five physical parameters for each spectrum in the library: effective temperature (
T
eff
), surface gravity (
log
g
), metallicity (Fe/H), microturbulent velocity (
log
(
v
micro
)
), and alpha-element abundance (
α
/Fe). These parameters are derived with a flexible data-driven algorithm that uses a neural network model. We train a neural network using the subset of 1675 MaStar targets that have also been observed in the Apache Point Observatory Galactic Evolution Experiment (APOGEE), adopting the independently-derived APOGEE Stellar Parameter and Chemical Abundance Pipeline parameters for this reference set. For the regions of parameter space not well represented by the APOGEE training set (7000 ≤
T
≤ 30,000 K), we supplement with theoretical model spectra. We present our derived parameters along with an analysis of the uncertainties and comparisons to other analyses from the literature.
Abstract
Recent wide-field integral-field spectroscopy has revealed the detailed properties of high-redshift Ly
α
nebulae, most often targeted due to the presence of an active galactic nucleus (AGN). ...Here, we use VLT/MUSE to resolve the morphology and kinematics of a nebula initially identified due to strong Ly
α
emission at
z
∼ 3.2 (LABn06). Our observations reveal a two-lobed Ly
α
nebula, at least ∼173 pkpc in diameter, with a light-weighted centroid near a mid-infrared source (within ≈17.2 pkpc) that appears to host an obscured AGN. The Ly
α
emission near the AGN is also coincident in velocity with the kinematic center of the nebula, suggesting that the nebula is both morphologically and kinematically centered on the AGN. Compared to AGN-selected Ly
α
nebulae, the surface-brightness profile of this nebula follows a typical exponential profile at large radii (>25 pkpc), although at small radii, the profile shows an unusual dip at the location of the AGN. The kinematics and asymmetry are similar to, and the C
iv
and He
ii
upper limits are consistent with, other AGN-powered Ly
α
nebulae. Double-peaked and asymmetric line profiles suggest that Ly
α
resonant scattering may be important in this nebula. These results support the picture of the AGN being responsible for powering a Ly
α
nebula that is oriented roughly in the plane of the sky. Further observations will explore whether the central surface-brightness depression is indicative of either an unusual gas or dust distribution or variation in the ionizing output of the AGN over time.
We use spatially extended measurements of Ly alpha as well as less optically thick emission lines from an asymptotically =80 kpc Ly alpha nebula at z asymptotically = 1.67 to assess the role of ...resonant scattering and to disentangle kinematic signatures from Ly alpha radiative transfer effects. We find that the Ly alpha , C IV, He II, and C III emission lines all tell a similar story in this system, and that the kinematics are broadly consistent with large-scale rotation. First, the observed surface brightness profiles are similar in extent in all four lines, strongly favoring a picture in which the Ly alpha photons are produced in situ instead of being resonantly scattered from a central source. Second, we see low kinematic offsets between Ly alpha and the less optically thick He II line (~100-200 km s super(-1)), providing further support for the argument that the Ly alpha and other emission lines are all being produced within the spatially extended gas. Finally, the full velocity field of the system shows coherent velocity shear in all emission lines: asymptotically =500 km s super(-1) over the central asymptotically =50 kpc of the nebula. The kinematic profiles are broadly consistent with large-scale rotation in a gas disk that is at least partially stable against collapse. These observations suggest that the Ly alpha nebula represents accreting material that is illuminated by an offset, hidden active galactic nucleus or distributed star formation, and that is undergoing rotation in a clumpy and turbulent gas disk. With an implied mass of M(< R = 20 kpc) ~ 3 x 10 super(11) M sub(middot in circle), this system may represent the early formation of a large Milky Way mass galaxy or galaxy group.
Abstract
It has been well established in the local universe that galaxy properties differ based on the large-scale environment in which they reside. As luminous Ly
α
nebulae have been shown to trace ...overdense environments at
z
∼ 2–3, comparing the properties of galaxies within Ly
α
nebulae systems to those in the field can provide insight into how and when locally observed trends between galaxy properties and environment emerged. Six Ly
α
nebulae were discovered at
z
∼ 2.3 in a blind search of the GOODS-S extragalactic field, a region also covered by the 3D-HST spectroscopic survey. Utilizing 3D-HST data, we identified 86 galaxies in the vicinity of these nebulae and used statistical tests to compare their physical properties to galaxies elsewhere in the field. Galaxies lying within 320 proper kpc of a Ly
α
nebula are roughly half a magnitude brighter than those in the field, with higher stellar masses, higher star formation rates, and larger effective radii. Even when considering the effects of sample incompleteness, our study suggests that galaxies in overdensities at
z
∼ 2.3 traced by Ly
α
nebulae are being influenced by their environment. Furthermore, Ly
α
-nebula-associated galaxies lie on the same main sequence of star formation as field galaxies but have a larger proportion of high-mass galaxies, consistent with the idea that galaxy evolution is accelerated in rich environments. Expanded surveys for Ly
α
nebulae in other deep extragalactic fields and galaxy spectroscopic follow-up with the James Webb Space Telescope (JWST) will better constrain the demographics of Ly
α
-nebula-associated galaxies.
Abstract
We report the detection of diffuse Ly
α
emission, or Ly
α
halos (LAHs), around star-forming galaxies at
z
≈ 3.78 and 2.66 in the NOAO Deep Wide-Field Survey Boötes field. Our samples ...consist of a total of ∼1400 galaxies, within two separate regions containing spectroscopically confirmed galaxy overdensities. They provide a unique opportunity to investigate how the LAH characteristics vary with host galaxy large-scale environment and physical properties. We stack Ly
α
images of different samples defined by these properties and measure their median LAH sizes by decomposing the stacked Ly
α
radial profile into a compact galaxy-like and an extended halo-like component. We find that the exponential scale-length of LAHs depends on UV continuum and Ly
α
luminosities, but not on Ly
α
equivalent widths or galaxy overdensity parameters. The full samples, which are dominated by low UV-continuum luminosity Ly
α
emitters (
M
UV
≳ −21), exhibit LAH sizes of 5–6 kpc. However, the most UV- or Ly
α-
luminous galaxies have more extended halos with scale-lengths of 7–9 kpc. The stacked Ly
α
radial profiles decline more steeply than recent theoretical predictions that include the contributions from gravitational cooling of infalling gas and from low-level star formation in satellites. However, the LAH extent matches what one would expect for photons produced in the galaxy and then resonantly scattered by gas in an outflowing envelope. The observed trends of LAH sizes with host galaxy properties suggest that the physical conditions of the circumgalactic medium (covering fraction, H
i
column density, and outflow velocity) change with halo mass and/or star formation rates.
Abstract
We investigate the effects of stellar populations and sizes on Ly
α
escape in 27 spectroscopically confirmed and 35 photometric Ly
α
emitters (LAEs) at
z
≈ 2.65 in seven fields of the Boötes ...region of the NOAO Deep Wide-Field Survey. We use deep HST/WFC3 imaging to supplement ground-based observations and infer key galaxy properties. Compared to typical star-forming galaxies (SFGs) at similar redshifts, the LAEs are less massive (
M
⋆
≈ 10
7
–10
9
M
⊙
), younger (ages ≲1 Gyr), smaller (
r
e
< 1 kpc), and less dust-attenuated (
E
(
B
−
V
) ≤ 0.26 mag) but have comparable star formation rates (SFRs ≈ 1–100
M
⊙
yr
−1
). Some of the LAEs in the sample may be very young galaxies having low nebular metallicities (
Z
neb
≲ 0.2
Z
⊙
) and/or high ionization parameters (
log
(
U
)
≳
−
2.4
). Motivated by previous studies, we examine the effects of the concentration of star formation and gravitational potential on Ly
α
escape by computing SFR surface density, Σ
SFR
, and specific SFR surface density, Σ
sSFR
. For a given Σ
SFR
, the Ly
α
escape fraction is higher for LAEs with lower stellar masses. The LAEs have a higher Σ
sSFR
, on average, compared to SFGs. Our results suggest that compact star formation in a low gravitational potential yields conditions amenable to the escape of Ly
α
photons. These results have important implications for the physics of Ly
α
radiative transfer and for the type of galaxies that may contribute significantly to cosmic reionization.
Abstract
A new but rare sample of spatially extended emission line nebulae, nicknamed “Green Beans,” was discovered at
z
≈ 0.3 thanks to strong O
iii
emission, and subsequently shown to be local ...cousins of the Ly
α
nebulae found at high redshift. Here we use follow-up APO/DIS spectroscopy to better understand how these low-redshift Ly
α
nebulae compare to other populations of strong emission line sources. Our spectroscopic data show that low-
z
Ly
α
nebulae have active galactic nucleus (AGN)-like emission line ratios, relatively narrow line widths (FWHM ≲ 1000 km s
−1
), and emission line kinematics resembling those of Type 2 AGN at the same redshift, confirming that they are powered by Type 2 AGN with typical ionizing continua. While low-
z
Ly
α
nebulae are larger and less concentrated than compact, star-forming Green Pea galaxies, we find that they resemble typical Type 2 AGN in terms of
r
-band concentration and size. Based on this pilot study, low-
z
Ly
α
nebulae appear to be a subset of Type 2 AGN with bluer optical continua and high O
iii
equivalent widths but with comparable sizes and similar O
iii
kinematics. These characteristics may simply reflect the fact that low-
z
Ly
α
nebulae are drawn from the high-luminosity end of the Type 2 AGN distribution, with higher nuclear activity driving higher O
iii
equivalent widths and more central star formation leading to bluer optical continua. Deeper spectroscopic follow-up of the full sample will shed further light on these issues and on the relationship between these low-
z
Ly
α
nebulae and the Ly
α
nebula population at high redshift.
Abstract
The discovery and spectroscopic confirmation of Hyperion, a protosupercluster at
z
∼ 2.47, provides an unprecedented opportunity to study distant galaxies in the context of their large-scale ...environment. We carry out deep narrowband imaging of a ≈1° × 1° region around Hyperion and select 157 Ly
α
emitters (LAEs). The inferred LAE overdensity is
δ
g
≈ 40 within an effective volume of 30 × 20 × 15 cMpc
3
, consistent with the fact that Hyperion is composed of multiple protoclusters and will evolve into a supercluster with a total mass of
M
tot
≈ 1.4 × 10
15
M
⊙
at
z
= 0. The distribution of LAEs closely mirrors that of known spectroscopic members, tracing the protocluster cores and extended filamentary arms connected to them, suggesting that they trace the same large-scale structure. By cross-correlating the LAE positions with H
i
tomography data, we find weak evidence that LAEs may be less abundant in the highest H
i
regions, perhaps because Ly
α
is suppressed in such regions. The Hyperion region hosts a large population of active galactic nuclei (AGNs) ≈ 12 times more abundant than that in the field. The prevalence of AGNs in protocluster regions hints at the possibility that they may be triggered by physical processes that occur more frequently in dense environments, such as galaxy mergers. Our study demonstrates LAEs as reliable markers of the largest cosmic structures. When combined with ongoing and upcoming imaging and spectroscopic surveys, wide-field narrowband imaging has the potential to advance our knowledge in the formation and evolution of cosmic structures and of their galaxy inhabitants.
Abstract
We explore the possibility and practical limitations of using a three-line approach to measure both the slope and normalization of the dust attenuation law in individual galaxies. To do ...this, we focus on a sample of 11 galaxies with existing ground-based Balmer H
α
and H
β
measurements from slit spectra, plus space-based grism constraints on Paschen-
β
. When accounting for observational uncertainties, we show that one galaxy has a well-constrained dust-law slope and normalization in the range expected from theoretical arguments; this galaxy therefore provides an example of what may be possible in the future. However, most of the galaxies are best fit by unusually steep or shallow slopes. We then explore whether additional astrophysical effects or observational biases could explain the elevated Paschen-
β
/H
α
ratios driving these results. We find that galaxies with high Paschen-
β
/H
α
ratios may be explained by slightly sub-unity covering fractions (>97%). Alternatively, differing slit losses for different lines can have a large impact on the results, emphasizing the importance of measuring all three lines with a consistent spectroscopic aperture. We conclude that, while the three-line approach to constraining the shape of the dust attenuation law in individual galaxies is promising, deep observations and a consistent observational strategy will be required to minimize observational biases and to disentangle the astrophysically interesting effect of differing covering fractions. The James Webb Space Telescope will provide more sensitive measurements of Balmer and Paschen lines for galaxies at
z
≈ 0.3–2, enabling uniform constraints on the optical–infrared dust attenuation law and its intrinsic variation.
We have studied the relationship between the star formation rate (SFR), surface density, and gas surface density in the spiral galaxy M51a (NGC 5194), using multiwavelength data obtained as part of ...the Spitzer Infrared Nearby Galaxies Survey (SINGS). We introduce a new SFR index based on a linear combination of Ha emission-line and 24 mu m continuum luminosities, which provides reliable extinction-corrected ionizing fluxes and SFR densities over a wide range of dust attenuations. The combination of these extinction-corrected SFR densities with aperture synthesis H I and CO maps has allowed us to probe the form of the spatially resolved star formation law on scales of 0.5-2 kpc. We find that the resolved SFR versus gas surface density relation is well represented by a Schmidt power law, which is similar in form and dispersion to the disk-averaged Schmidt law. We observe a comparably strong correlation of the SFR surface density with the molecular gas surface density, but no significant correlation with the surface density of atomic gas. The best-fitting slope of the Schmidt law varies from N = 1.37 to 1.56, with zero point and slope that change systematically with the spatial sampling scale. We tentatively attribute these variations to the effects of areal sampling and averaging of a nonlinear intrinsic star formation law. Our data can also be fitted by an alternative parameterization of the SFR surface density in terms of the ratio of gas surface density to local dynamical time, but with a considerable dispersion.
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