446 research outputs found
Feeding the fire: Tracing the mass-loading of 10^7 K galactic outflows with O VI absorption
Galactic outflows regulate the amount of gas galaxies convert into stars.
However, it is difficult to measure the mass outflows remove because they span
a large range of temperatures and phases. Here, we study the rest-frame
ultraviolet spectrum of a lensed galaxy at z~2.9 with prominent interstellar
absorption lines from O I, tracing neutral gas, up to O VI, tracing
transitional phase gas. The O VI profile mimics weak low-ionization profiles at
low velocities, and strong saturated profiles at high velocities. These trends
indicate that O VI gas is co-spatial with the low-ionization gas. Further, at
velocities blueward of -200 km/s the column density of the low-ionization
outflow rapidly drops while the O VI column density rises, suggesting that O VI
is created as the low-ionization gas is destroyed. Photoionization models do
not reproduce the observed O VI, but adequately match the low-ionization gas,
indicating that the phases have different formation mechanisms. Photoionized
outflows are more massive than O VI outflows for most of the observed
velocities, although the O VI mass outflow rate exceeds the photoionized
outflow at velocities above the galaxy's escape velocity. Therefore, most gas
capable of escaping the galaxy is in a hot outflow phase. We suggest that the O
VI absorption is a temporary by-product of conduction transferring mass from
the photoionized phase to an unobserved hot wind, and discuss how this
mass-loading impacts the observed circum-galactic medium.Comment: 17 pages, 12 figures, accepted for publication in MNRA
How Future Space-Based Weak Lensing Surveys Might Obtain Photometric Redshifts Independently
We study how the addition of on-board optical photometric bands to future
space-based weak lensing instruments could affect the photometric redshift
estimation of galaxies, and hence improve estimations of the dark energy
parameters through weak lensing. Basing our study on the current proposed
Euclid configuration and using a mock catalog of galaxy observations, various
on-board options are tested and compared with the use of ground-based
observations from the Large Synoptic Survey Telescope (LSST) and Pan-STARRS.
Comparisons are made through the use of the dark energy Figure of Merit, which
provides a quantifiable measure of the change in the quality of the scientific
results that can be obtained in each scenario. Effects of systematic offsets
between LSST and Euclid photometric calibration are also studied. We find that
adding two (U and G) or even one (U) on-board optical band-passes to the
space-based infrared instrument greatly improves its photometric redshift
performance, bringing it close to the level that would be achieved by combining
observations from both space-based and ground-based surveys while freeing the
space mission from reliance on external datasets.Comment: Accepted for publication in PASP. A high-quality version of Fig 1 can
be found on http://www.ap.smu.ca/~sawicki/DEphoto
Connection Between the Circumgalactic Medium and the Interstellar Medium of Galaxies: Results from the COS-GASS Survey
We present a study exploring the nature and properties of the Circum-Galactic
Medium (CGM) and its connection to the atomic gas content in the interstellar
medium (ISM) of galaxies as traced by the HI 21cm line. Our sample includes 45
low-z (0.026-0.049) galaxies from the GALEX Arecibo SDSS Survey. Their CGM was
probed via absorption in the spectra of background Quasi-Stellar Objects at
impact parameters of 63 to 231kpc. The spectra were obtained with the Cosmic
Origins Spectrograph aboard the Hubble Space Telescope. We detected neutral
hydrogen (Ly absorption-lines) in the CGM of 92% of the galaxies. We
find the radial profile of the CGM as traced by the Ly equivalent width
can be fit as an exponential with a scale length of roughly the virial radius
of the dark matter halo. We found no correlation between the orientation of
sightline relative to the galaxy major axis and the Ly equivalent
width. The velocity spread of the circumgalactic gas is consistent with that
seen in the atomic gas in the interstellar medium. We find a strong correlation
(99.8% confidence) between the gas fraction (M(HI)/M*) and the
impact-parameter-corrected Ly equivalent width. This is stronger than
the analogous correlation between corrected Ly equivalent width and
SFR/M* (97.5% confidence). These results imply a physical connection between
the HI disk and the CGM, which is on scales an order-of-magnitude larger. This
is consistent with the picture in which the HI disk is nourished by accretion
of gas from the CGM.Comment: 13 pages, 9 figures, and 2 tables. Submitted to Ap
A Deep Search For Faint Galaxies Associated With Very Low-redshift C IV Absorbers: III. The Mass- and Environment-dependent Circumgalactic Medium
Using Hubble Space Telescope Cosmic Origins Spectrograph observations of 89
QSO sightlines through the Sloan Digital Sky Survey footprint, we study the
relationships between C IV absorption systems and the properties of nearby
galaxies as well as large-scale environment. To maintain sensitivity to very
faint galaxies, we restrict our sample to 0.0015 < z < 0.015, which defines a
complete galaxy survey to L > 0.01 L* or stellar mass log M_* > 8 Msun. We
report two principal findings. First, for galaxies with impact parameter rho <
1 rvir, C IV detection strongly depends on the luminosity/stellar mass of the
nearby galaxy. C IV is preferentially associated with galaxies with log M_* >
9.5 Msun; lower mass galaxies rarely exhibit significant C IV absorption
(covering fraction f = 9 +12-6% for 11 galaxies with log M_* < 9.5 Msun).
Second, C IV detection within the log M_* > 9.5 Msun population depends on
environment. Using a fixed-aperture environmental density metric for galaxies
with rho < 160 kpc at z < 0.055, we find that 57+/-12% (8/14) of galaxies in
low-density regions (regions with fewer than seven L > 0.15 L* galaxies within
1.5 Mpc) have affiliated C IV absorption; however, none (0/7) of the galaxies
in denser regions show C IV. Similarly, the C IV detection rate is lower for
galaxies residing in groups with dark-matter halo masses of log Mhalo > 12.5
Msun. In contrast to C IV, H I is pervasive in the CGM without regard to mass
or environment. These results indicate that C IV absorbers with log N(C IV) >
13.5 cm^-2 trace the halos of log M_* > 9.5 Msun galaxies but also reflect
larger scale environmental conditions.Comment: 26 pages, 13 figures. ApJ, in pres
Unravelling multi-temperature dust populations in the dwarf galaxy Holmberg II
Holmberg II - a dwarf galaxy in the nearby M81 group - is a very informative
source of distribution of gas and dust in the interstellar discs.
High-resolution observations in the infrared (IR) allows us to distinguish
isolated star-forming regions, photodissociation (PDR) and HII regions,
remnants of supernovae (SNe) explosions and, as such, can provide information
about more relevant physical processes. In this paper we analyse dust emission
in the wavelength range 4.5 to 160 micron using the data from IR space
observatories at 27 different locations across the galaxy. We observe that the
derived spectra can be represented by multiple dust populations with different
temperatures, which are found to be independent of their locations in the
galaxy. By comparing the dust temperatures with the far ultraviolet (FUV)
intensities observed by the UVIT instrument onboard AstroSat, we find that for
locations showing a 100 micron peak, the temperature of cold (20 to 30 K) dust
grains show a dependence on the FUV intensities, while such dependence is not
observed for the other locations. We believe that the approach described here
can be a good tool in revealing different dust populations in other nearby
galaxies with available high spatial resolution data.Comment: 7 pages, 4 figures, submitted to Letters to MNRA
Montmorillonite K-10 as a reusable catalyst for fischer type of glycosylation under microwave irradiation
Travel and Insight on the Limen: A Content Analysis of Adventure Travel Narratives
Travel narratives, both historical and modern, depict a hero’s quest for insight and self-discovery where the outward journey is a literal and metaphorical search for one’s authentic self, spirituality, and life’s meaning. This article reports the results of a study that examined the association between travel’s liminal experience and insight. Using content analysis of 50 published adventure travel narratives, a significant association between insight and liminality was identified, and the tentative conclusion that liminal experience may be a stimulus for insight was made. Variables (solo/group travel, travel motivation, gender, and cultural novelty) hypothesized to moderate the association between liminality and insight were also explored. Hierarchical log linear modeling identified only one significant three-way association: travel motive. Travelers who sought to escape negative associations with home were less likely to experience liminality and insight than those who were motivated to travel for other reasons
- …