Abstract
Observed breakBRD (“break bulges in red disks”) galaxies are a nearby sample of face-on disk galaxies with particularly centrally concentrated star formation: they have red disks but recent ...star formation in their centers as measured by the D
n
4000 spectral index. In Kopenhafer et al., a comparable population of breakBRD analogs was identified in the TNG simulation, in which the central concentration of star formation was found to reflect a central concentration of dense, star-forming gas caused by a lack of dense gas in the galaxy outskirts. In this paper, we examine the circumgalactic medium of the central breakBRD analogs to determine if the extended halo gas also shows differences from that around comparison galaxies with comparable stellar mass. We examine the circumgalactic medium gas mass, specific angular momentum, and metallicity in these galaxy populations. We find less gas in the circumgalactic medium of breakBRD galaxies, and that the breakBRD circumgalactic medium is slightly more concentrated than that of comparable
M
*
galaxies. In addition, we find that the angular momentum in the circumgalactic medium of breakBRD galaxies tends to be low for their stellar mass, and shows more misalignment to the angular momentum vector of the stellar disk. Finally, we find that the circumgalactic medium metallicity of breakBRD galaxies tends to be high for their stellar mass. Together with their low star formation rate, we argue that these circumgalactic medium properties indicate a small amount of disk feeding concentrated in the central regions and a lack of low-metallicity gas accretion from the intergalactic medium.
Abstract
We assemble a sample of 17 low-metallicity (7.45 < log(O/H)+12 < 8.12) galaxies with
z
≲ 0.1 found spectroscopically, without photometric preselection, in early data from the Hobby–Eberly ...Telescope Dark Energy Experiment. Star-forming galaxies that occupy the lowest-mass and lowest-metallicity end of the mass–metallicity relation tend to be undersampled in continuum-based surveys as their spectra are typically dominated by emission from newly forming stars. We search for galaxies with high O
iii
λ
5007/O
ii
λ
3727, implying highly ionized nebular emission often indicative of low-metallicity systems. With the Second Generation Low Resolution Spectrograph on the Hobby–Eberly Telescope we acquired follow-up spectra, with higher resolution and broader wavelength coverage, of each low-metallicity candidate in order to confirm the redshift, measure the H
α
and N
ii
line strengths, and, in many cases, obtain deeper spectra of the blue lines. We find our galaxies are consistent with the mass–metallicity relation of typical low-mass galaxies. However, galaxies in our sample tend to have similar specific star formation rates as the incredibly rare “blueberry” galaxies found by Yang et al. We illustrate the power of spectroscopic surveys for finding low-mass and low-metallicity galaxies and reveal that we find a sample of galaxies that are a hybrid between the properties of typical dwarf galaxies and the more extreme blueberry galaxies.
Abstract
The Hobby–Eberly Telescope (HET) Dark Energy Experiment (HETDEX) is undertaking a blind wide-field low-resolution spectroscopic survey of 540 deg
2
of sky to identify and derive redshifts ...for a million Ly
α
-emitting galaxies in the redshift range 1.9 <
z
< 3.5. The ultimate goal is to measure the expansion rate of the universe at this epoch, to sharply constrain cosmological parameters and thus the nature of dark energy. A major multiyear Wide-Field Upgrade (WFU) of the HET was completed in 2016 that substantially increased the field of view to 22′ diameter and the pupil to 10 m, by replacing the optical corrector, tracker, and Prime Focus Instrument Package and by developing a new telescope control system. The new, wide-field HET now feeds the Visible Integral-field Replicable Unit Spectrograph (VIRUS), a new low-resolution integral-field spectrograph (LRS2), and the Habitable Zone Planet Finder, a precision near-infrared radial velocity spectrograph. VIRUS consists of 156 identical spectrographs fed by almost 35,000 fibers in 78 integral-field units arrayed at the focus of the upgraded HET. VIRUS operates in a bandpass of 3500−5500 Å with resolving power
R
≃ 800. VIRUS is the first example of large-scale replication applied to instrumentation in optical astronomy to achieve spectroscopic surveys of very large areas of sky. This paper presents technical details of the HET WFU and VIRUS, as flowed down from the HETDEX science requirements, along with experience from commissioning this major telescope upgrade and the innovative instrumentation suite for HETDEX.
Abstract
Supernova (SN) 2023ixf was discovered on 2023 May 19. The host galaxy, M101, was observed by the Hobby–Eberly Telescope Dark Energy Experiment collaboration over the period 2020 April ...30–2020 July 10, using the Visible Integral-field Replicable Unit Spectrograph (3470 ≲
λ
≲ 5540 Å) on the 10 m Hobby–Eberly Telescope. The fiber filling factor within ±30″ of SN 2023ixf is 80% with a spatial resolution of 1″. The
r
< 5.″5 surroundings are 100% covered. This allows us to analyze the spatially resolved preexplosion local environments of SN 2023ixf with nebular emission lines. The two-dimensional maps of the extinction and the star formation rate (SFR) surface density (Σ
SFR
) show weak increasing trends in the radial distributions within the
r
< 5.″5 regions, suggesting lower values of extinction and SFR in the vicinity of the progenitor of SN 2023ixf. The median extinction and that of the surface density of SFR within
r
< 3″ are
E
(
B
−
V
) = 0.06 ± 0.14, and
Σ
SFR
=
10
−
5.44
±
0.66
M
☉
yr
−
1
arcsec
−
2
.
There is no significant change in extinction before and after the explosion. The gas metallicity does not change significantly with the separation from SN 2023ixf. The metal-rich branch of the
R
23
calculations indicates that the gas metallicity around SN 2023ixf is similar to the solar metallicity (∼
Z
☉
). The archival deep images from the Canada–France–Hawaii Telescope Legacy Survey (CFHTLS) show a clear detection of the progenitor of SN 2023ixf in the
z
band at 22.778 ± 0.063 mag, but nondetections in the remaining four bands of CFHTLS (
u
,
g
,
r
,
i
). The results suggest a massive progenitor of ≈22
M
☉
.
Abstract
We describe the ensemble properties of the 1.9 <
z
< 3.5 Lyman alpha emitters (LAEs) found in the HETDEX survey’s first public data release, HETDEX Public Source Catalog 1. Stacking the ...low-resolution (
R
∼ 800) spectra greatly increases the signal-to-noise ratio (S/N), revealing spectral features otherwise hidden by noise, and we show that the stacked spectrum is representative of an average member of the set. The flux-limited, Ly
α
S/N restricted stack of 50,000 HETDEX LAEs shows the ensemble biweight
average
z
∼ 2.6 LAE to be a blue (UV continuum slope ∼ −2.4 and
E(B – V)
< 0.1), moderately bright (
M
UV
∼ −19.7) star-forming galaxy with strong Ly
α
emission (log
L
Ly
α
∼ 42.8 and
W
λ
(Ly
α
) ∼ 114 Å), and potentially significant leakage of ionizing radiation. The rest-frame UV light is dominated by a young, metal-poor stellar population with an average age of 5–15 Myr and metallicity of 0.2–0.3
Z
⊙
.
Abstract
The Hobby–Eberly Telescope Dark Energy Experiment (HETDEX) is an untargeted spectroscopic survey that aims to measure the expansion rate of the universe at
z
∼ 2.4 to 1% precision for both
H
...(
z
) and
D
A
(
z
). HETDEX is in the process of mapping in excess of one million Ly
α
emitting (LAE) galaxies and a similar number of lower-
z
galaxies as a tracer of the large-scale structure. The success of the measurement is predicated on the post-observation separation of galaxies with Ly
α
emission from the lower-
z
interloping galaxies, primarily O
ii
, with low contamination and high recovery rates. The Emission Line eXplorer (ELiXer) is the principal classification tool for HETDEX, providing a tunable balance between contamination and completeness as dictated by science needs. By combining multiple selection criteria, ELiXer improves upon the 20 Å rest-frame equivalent width cut commonly used to distinguish LAEs from lower-
z
O
ii
emitting galaxies. Despite a spectral resolving power,
R
∼ 800, that cannot resolve the O
ii
doublet, we demonstrate the ability to distinguish LAEs from foreground galaxies with 98.1% accuracy. We estimate a contamination rate of Ly
α
by O
ii
of 1.2% and a Ly
α
recovery rate of 99.1% using the default ELiXer configuration. These rates meet the HETDEX science requirements.
We introduce a collection of primarily centrally star-forming galaxies that are selected by disk color to have truncated disk star formation. We show that common explanations for centrally ...concentrated star formation-low stellar mass, bars, and high-density environments-do not universally apply to this sample. To gain insight into our sample, we compare these galaxies to a parent sample of strongly star-forming galaxies and to a parent sample of galaxies with low specific star formation rates. We find that in star formation and color space from ultraviolet to the infrared these galaxies either fall between the two samples or agree more closely with galaxies with high specific star formation rates. Their morphological characteristics also lie between high and low specific star formation rate galaxies, although their Petrosian radii agree well with that of the low specific star formation rate parent sample. We discuss whether this sample is likely to be quenching or showing an unusual star formation distribution while continuing to grow through star formation. Future detailed studies of these galaxies will give us insights into how the local conditions within a galaxy balance environmental influence to govern the distribution of star formation. In this first paper in a series, we describe the global properties that identify this sample as separate from more average spiral galaxies, and we identify paths forward to explore the underlying causes of their differences.
The habenula and interpeduncular nucleus (IPN) are part of a dorsal diencephalic conduction system which receives input from cholinergic, striatal, and hypothalamic areas, and sends output to ...several, disparate midbrain regions. These output regions include the dorsal tegmental nucleus, which is part of a navigation-related system that provides a signal for directional heading. The habenula and IPN also project to the dorsal and medial Raphe nuclei, thought to be involved in mood and behavioral state regulation. Here, cells in both the habenula and IPN were recorded in freely moving rats while they foraged for food pellets. There were four major findings. First, many of the cells tended to fire in sporadic bouts of relatively high versus low rates, and this may be related to intrinsic cell properties discovered during in vitro studies. Second, although these regions are connected to the direction signaling circuit, they do not, themselves demonstrate a directional signal. Third, about 10% of the cells in the lateral habenula showed a strong correlation between rate and angular head motion. This may constitute an important, requisite input to the above-mentioned head direction circuit. Finally, many of the cells in each region showed a temporally coarse correlation with running speed, so that bouts of high frequency firing coincided with episodes of higher behavioral activation. This last finding may be related to work which shows an influence of the habenula on locomotor activity, and in relation to the protective effects of exercise in relation to stress, as mediated by the Raphe nuclei.
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