145 research outputs found
Galaxies Probing Galaxies at High Resolution: Co-Rotating Gas Associated with a Milky Way Analog at z=0.4
We present results on gas flows in the halo of a Milky Way-like galaxy at
z=0.413 based on high-resolution spectroscopy of a background galaxy. This is
the first study of circumgalactic gas at high spectral resolution towards an
extended background source (i.e., a galaxy rather than a quasar). Using
longslit spectroscopy of the foreground galaxy, we observe spatially extended H
alpha emission with circular rotation velocity v=270 km/s. Using echelle
spectroscopy of the background galaxy, we detect Mg II and Fe II absorption
lines at impact parameter rho=27 kpc that are blueshifted from systemic in the
sense of the foreground galaxy's rotation. The strongest absorber EW(2796) =
0.90 A has an estimated column density (N_H>10^19 cm-2) and line-of-sight
velocity dispersion (sigma=17 km/s) that are consistent with the observed
properties of extended H I disks in the local universe. Our analysis of the
rotation curve also suggests that this r=30 kpc gaseous disk is warped with
respect to the stellar disk. In addition, we detect two weak Mg II absorbers in
the halo with small velocity dispersions (sigma<10 km/s). While the exact
geometry is unclear, one component is consistent with an extraplanar gas cloud
near the disk-halo interface that is co-rotating with the disk, and the other
is consistent with a tidal feature similar to the Magellanic Stream. We can
place lower limits on the cloud sizes (l>0.4 kpc) for these absorbers given the
extended nature of the background source. We discuss the implications of these
results for models of the geometry and kinematics of gas in the circumgalactic
medium.Comment: 14 pages, 6 figures, submitted to ApJ, comments welcom
The Excitation of Extended Red Emission: New Constraints on its Carrier From HST Observations of NGC 7023
The carrier of the dust-associated photoluminescence process causing the
extended red emission (ERE) in many dusty interstellar environments remains
unidentified. Several competing models are more or less able to match the
observed broad, unstructured ERE band. We now constrain the character of the
ERE carrier further by determining the wavelengths of the radiation that
initiates the ERE. Using the imaging capabilities of the Hubble Space
Telescope, we have resolved the width of narrow ERE filaments appearing on the
surfaces of externally illuminated molecular clouds in the bright reflection
nebula NGC 7023 and compared them with the depth of penetration of radiation of
known wavelengths into the same cloud surfaces. We identify photons with
wavelengths shortward of 118 nm as the source of ERE initiation, not to be
confused with ERE excitation, however. There are strong indications from the
well-studied ERE in the Red Rectangle nebula and in the high-|b| Galactic
cirrus that the photon flux with wavelengths shortward of 118 nm is too small
to actually excite the observed ERE, even with 100% quantum efficiency. We
conclude, therefore, that ERE excitation results from a two-step process. While
none of the previously proposed ERE models can match these new constraints, we
note that under interstellar conditions most polycyclic aromatic hydrocarbon
(PAH) molecules are ionized to the di-cation stage by photons with E > 10.5 eV
and that the electronic energy level structure of PAH di-cations is consistent
with fluorescence in the wavelength band of the ERE. Therefore, PAH di-cations
deserve further study as potential carriers of the ERE. (abridged)Comment: Accepted for Publication in the Ap
The Space Density of Intermediate-redshift, Extremely Compact, Massive Starburst Galaxies
© 2022. The Author(s). Published by the American Astronomical Society. This is an open access article distributed under the Creative Commons Attribution License, to view a copy of the license, see: https://creativecommons.org/licenses/by/4.0/https://creativecommons.org/licenses/by/4.0/We present a measurement of the intrinsic space density of intermediate-redshift (z ⌠0.5), massive (M * ⌠1011 M â), compact (R e ⌠100 pc) starburst (ÎŁSFR ⌠1000 M â yrâ1 kpcâ1) galaxies with tidal features indicative of them having undergone recent major mergers. A subset of them host kiloparsec-scale, > 1000 km sâ1 outflows and have little indication of AGN activity, suggesting that extreme star formation can be a primary driver of large-scale feedback. The aim for this paper is to calculate their space density so we can place them in a better cosmological context. We do this by empirically modeling the stellar populations of massive, compact starburst galaxies. We determine the average timescale on which galaxies that have recently undergone an extreme nuclear starburst would be targeted and included in our spectroscopically selected sample. We find that massive, compact starburst galaxies targeted by our criteria would be selectable for âŒ148â24+27 Myr and have an intrinsic space density nCSâŒ(1.1â0.3+0.5)Ă10â6Mpcâ3 . This space density is broadly consistent with our z ⌠0.5 compact starbursts being the most extremely compact and star-forming low-redshift analogs of the compact star-forming galaxies in the early universe, as well as them being the progenitors to a fraction of intermediate-redshift, post-starburst, and compact quiescent galaxies.Peer reviewe
Kinematics, Structure, and Mass Outflow Rates of Extreme Starburst Galactic Outflows
We present results on the properties of extreme gas outflows in massive (10), compact, starburst () galaxies at z = with very high star
formation surface densities ($2000 \,\rm M_{\odot} \
yr^{-1} \ kpc^{-2}820 - 2860
\kmps. High-resolution spectroscopy allows us to measure precise column
densities and covering fractions as a function of outflow velocity and
characterize the kinematics and structure of the cool gas outflow phase (T
\sim^4 K). We find substantial variation in the absorption profiles,
which likely reflects the complex morphology of inhomogeneously-distributed,
clumpy gas and the intricacy of the turbulent mixing layers between the cold
and hot outflow phases. There is not a straightforward correlation between the
bursts in the galaxies' star formation histories and their wind absorption line
profiles, as might naively be expected for starburst-driven winds. The lack of
strong \mgii \ absorption at the systemic velocity is likely an orientation
effect, where the observations are down the axis of a blowout. We infer high
mass outflow rates of \rm \sim-\rm M_{\odot} \, yr^{-1}\eta\sim\eta\sim$20 for two galaxies. While
these values have high uncertainties, they suggest that starburst galaxies are
capable of ejecting very large amounts of cool gas that will substantially
impact their future evolution.Comment: Accepted for publication in The Astrophysical Journa
Ionized Gas Extended Over 40 kpc in an Odd Radio Circle Host Galaxy
A new class of extragalactic astronomical sources discovered in 2021, named
Odd Radio Circles (ORCs, Norris et al. 2021), are large rings of faint, diffuse
radio continuum emission spanning ~1 arcminute on the sky. Galaxies at the
centers of several ORCs have photometric redshifts of z~0.3-0.6, implying
physical scales of several 100 kiloparsecs in diameter for the radio emission,
the origin of which is unknown. Here we report spectroscopic data on an ORC
including strong [OII] emission tracing ionized gas in the central galaxy of
ORC4 at z=0.4512. The physical extent of the [OII] emission is ~40 kpc in
diameter, larger than expected for a typical early-type galaxy (Pandya et al,
2017) but an order of magnitude smaller than the large-scale radio continuum
emission. We detect a ~200 km/s velocity gradient across the [OII] nebula, as
well as a high velocity dispersion of ~180 km/s. The [OII] equivalent width
(EW, ~50 Ang) is extremely high for a quiescent galaxy. The morphology,
kinematics, and strength of the [OII] emission are consistent with the infall
of shock ionized gas near the galaxy, following a larger-scale, outward moving
shock driven by a galactic wind. Both the extended optical and radio emission,
while observed on very different scales, may therefore result from the same
dramatic event.Comment: 7 figures, accepted to Natur
B-lymphocyte heterogeneity: development and characterization of an alloantiserum which distinguishes B-lymphocyte differentiation alloantigens.
The Ionization and Dynamics of the Makani Galactic Wind
© 2023 The Author(s). Published by the American Astronomical Society. This is an open access article distributed under the Creative Commons Attribution License, to view a copy of the license, see: https://creativecommons.org/licenses/by/4.0/The Makani galaxy hosts the poster child of a galactic wind on scales of the circumgalactic medium. It consists of a two-episode wind in which the slow, outer wind originated 400 Myr ago (Episode I; R I = 20 â 50 kpc) and the fast, inner wind is 7 Myr old (Episode II; R II = 0 â 20 kpc). While this wind contains ionized, neutral, and molecular gas, the physical state and mass of the most extended phaseâthe warm, ionized gasâare unknown. Here we present Keck optical spectra of the Makani outflow. These allow us to detect hydrogen lines out to r = 30â40 kpc and thus constrain the mass, momentum, and energy in the wind. Many collisionally excited lines are detected throughout the wind, and their line ratios are consistent with 200â400 km sâ1 shocks that power the ionized gas, with v shock = Ï wind. Combining shock models, density-sensitive line ratios, and mass and velocity measurements, we estimate that the ionized mass and outflow rate in the Episode II wind could be as high as those of the molecular gas: MIIHIIâŒMIIH2=(1â2)Ă109Mâ and dM/dtIIHIIâŒdM/dtIIH2=170â250Mâ yrâ1. The outer wind has slowed, so that dM/dtIHIIâŒ10Mâ yrâ1, but it contains more ionized gas, MIHII=5Ă109 M â. The momentum and energy in the recent Episode II wind imply a momentum-driven flow (p âboostâ âŒ7) driven by the hot ejecta and radiation pressure from the Eddington-limited, compact starburst. Much of the energy and momentum in the older Episode I wind may reside in a hotter phase, or lie further into the circumgalactic medium.Peer reviewe
Physical Properties of Massive Compact Starburst Galaxies with Extreme Outflows
© 2021. The Author(s). Published by the American Astronomical Society. This is an Open Access article, distributed under the terms of the Creative Commons Attribution 4.0 licence. https://creativecommons.org/licenses/by/4.0/We present results on the nature of extreme ejective feedback episodes and the physical conditions of a population of massive (M * ⌠1011 M â), compact starburst galaxies at z = 0.4â0.7. We use data from Keck/NIRSPEC, SDSS, Gemini/GMOS, MMT, and Magellan/MagE to measure rest-frame optical and near-IR spectra of 14 starburst galaxies with extremely high star formation rate surface densities (mean ÎŁSFR ⌠2000 M â yrâ1 kpcâ2) and powerful galactic outflows (maximum speeds v 98 ⌠1000â3000 km sâ1). Our unique data set includes an ensemble of both emission ([O ii] λλ3726,3729, HÎČ, [O iii] λλ4959,5007, Hα, [N ii] λλ6549,6585, and [S ii] λλ6716,6731) and absorption (Mg ii λλ2796,2803, and Fe ii λ2586) lines that allow us to investigate the kinematics of the cool gas phase (T ⌠104 K) in the outflows. Employing a suite of line ratio diagnostic diagrams, we find that the central starbursts are characterized by high electron densities (median n e ⌠530 cmâ3), and high metallicity (solar or supersolar). We show that the outflows are most likely driven by stellar feedback emerging from the extreme central starburst, rather than by an AGN. We also present multiple intriguing observational signatures suggesting that these galaxies may have substantial Lyman continuum (LyC) photon leakage, including weak [S ii] nebular emission lines. Our results imply that these galaxies may be captured in a short-lived phase of extreme star formation and feedback where much of their gas is violently blown out by powerful outflows that open up channels for LyC photons to escape.Peer reviewedFinal Published versio
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