264 research outputs found
On The Nature of Ring Patterns In Ice Crystals of Hailstones: A Signature of Global Warming
In the present work we report for the first time the ring patterns in the ice crystals procured from hailstones at Doom Dooma (27.40N, 95.30E) on March 17, 2016 and April 9, 2017. We have measured the intensity patterns of the rings with the help of a software (ImageJ). Since the ring patterns have been observed in the ice crystals of hailstones only in recent years, it is reasonable to believe that they will give valuable information on the process of ice nucleation and possibly on global warming
Spatially Resolved Galactic Wind in Lensed Galaxy RCSGA 032727-132609
We probe the spatial distribution of outflowing gas along four lines of sight
separated by up to 6 kpc in a gravitationally-lensed star-forming galaxy at
z=1.70. Using MgII and FeII emission and absorption as tracers, we find that
the clumps of star formation are driving galactic outflows with velocities of
-170 to -250 km/sec. The velocities of MgII emission are redshifted with
respect to the systemic velocities of the galaxy, consistent with being
back-scattered. By contrast, the FeII fluorescent emission lines are either
slightly blueshifted or at the systemic velocity of the galaxy. Taken together,
the velocity structure of the MgII and FeII emission is consistent with arising
through scattering in galactic winds. Assuming a thin shell geometry for the
out owing gas, the estimated masses carried out by these outfows are large (>
30 - 50 ), with mass loading factors several times the
star-formation rate. Almost 20% to 50% of the blueshifted absorption probably
escapes the gravitational potential of the galaxy. In this galaxy, the outflow
is "locally sourced", that is, the properties of the outflow in each line of
sight are dominated by the properties of the nearest clump of star formation;
the wind is not global to the galaxy. The mass outflow rates and the momentum
flux carried out by outflows in individual star forming knots of this object
are comparable to that of starburst galaxies in the local Universe.Comment: 19 pages, 10 figure, accepted for publication in MNRA
The Properties of the Circumgalactic Medium in Red and Blue Galaxies: Results from the COS-GASS+COS-HALOS Surveys
We use the combined data from the COS-GASS and COS-Halos surveys to characterize the Circum-Galactic Medium (CGM) surrounding typical low-redshift galaxies in the mass range , and over a range of impact parameters extending to just beyond the halo virial radius (R vir). We find the radial scale length of the distributions of the equivalent widths of the Lyα and Si iii absorbers to be ~1 and ~0.4 R vir, respectively. The radial distribution of equivalent widths is relatively uniform for the blue galaxies, but highly patchy (i.e., it has a low covering fraction) for the red galaxies. We also find that the Lyα and Si iii equivalent widths show significant positive correlations with the specific star formation rate (sSFR) of the galaxy. We find a surprising lack of correlations between the halo mass (virial velocity) and either the velocity dispersions or velocity offsets of the Lyα lines. The ratio of the velocity offset to the velocity dispersion for the Lyα absorbers has a mean value of ~4, suggesting that a given line of sight is intersecting a dynamically coherent structure in the CGM, rather than a sea of orbiting clouds. The kinematic properties of the CGM are similar in the blue and red galaxies, although we find that a significantly larger fraction of the blue galaxies have large Lyα velocity offsets (>200 km s−1). We show that—if the CGM clouds represent future fuel for star formation—our new results could imply a large drop in the sSFR across the galaxy mass-range we probe
Spatially Resolved Patchy Lyman- Emission Within the Central Kiloparsec of a Strongly Lensed Quasar Host Galaxy at z = 2.8
We report the detection of extended Lyman- emission from the host
galaxy of SDSS~J2222+2745, a strongly lensed quasar at . Spectroscopic
follow-up clearly reveals extended Lyman- in emission between two
images of the central active galactic nucleus (AGN). We reconstruct the lensed
quasar host galaxy in the source plane by applying a strong lens model to HST
imaging, and resolve spatial scales as small as 200 parsecs. In the
source plane we recover the host galaxy morphology to within a few hundred
parsecs of the central AGN, and map the extended Lyman- emission to its
physical origin on one side of the host galaxy at radii 0.5-2 kpc from
the central AGN. There are clear morphological differences between the
Lyman- and rest-frame ultraviolet stellar continuum emission from the
quasar host galaxy. Furthermore, the relative velocity profiles of quasar
Lyman-, host galaxy Lyman-, and metal lines in outflowing gas
reveal differences in the absorbing material affecting the AGN and host galaxy.
These data indicate the presence of patchy local intervening gas in front of
the central quasar and its host galaxy. This interpretation is consistent with
the central luminous quasar being obscured across a substantial fraction of its
surrounding solid angle, resulting in strong anisotropy in the exposure of the
host galaxy to ionizing radiation from the AGN. This work demonstrates the
power of strong lensing-assisted studies to probe spatial scales that are
currently inaccessible by other means.Comment: Accepted to ApJ Letters; 7 pages, 5 figure
A 30 kpc Spatially Extended Clumpy and Asymmetric Galactic Outflow at z 1.7
We image the spatial extent of a cool galactic outflow with fine structure Fe
II emission and resonant Mg II emission in a gravitationally lensed
star-forming galaxy at . The Fe II and Mg II
(continuum-subtracted) emissions span out to radial distances of 14.33
kpc and 26.5 kpc, respectively, with maximum spatial extents of 21 kpc
for Fe II emission and 30 kpc for Mg II emission. Mg II residual
emission is patchy and covers a total area of 184 kpc, constraining
the minimum area covered by the outflowing gas to be 13% of the total
area. Mg II emission is asymmetric and shows 21% more extended emission
along the declination direction. We constrain the covering fractions of the Fe
II and Mg II emission as a function of radial distance and characterize
them with a power law model. The Mg II 2803 emission line shows two
kinematically distinct emission components, and may correspond to two distinct
shells of outflowing gas with a velocity separation of 400
km/s. By using multiple images with different magnifications of the galaxy in
the image plane, we trace the Fe II, Mg II emissions around three
individual star-forming regions. In all cases, both the Fe II and Mg II
emissions are more spatially extended compared to the star forming regions
traced by the [O II] emission. These findings provide robust constraints on the
spatial extent of the outflowing gas, and combined with outflow velocity and
column density measurements will give stringent constraints on mass outflow
rates of the galaxy.Comment: 22 pages, 14 figures, 4 tables, accepted to ApJ, the referee comments
are incorporated in this versio
Dissecting a 30 kpc galactic outflow at 1.7
We present the spatially resolved measurements of a cool galactic outflow in
the gravitationally lensed galaxy RCS0327 at using VLT/MUSE
IFU observations. We probe the cool outflowing gas, traced by blueshifted Mg II
and Fe II absorption lines, in 15 distinct regions of the same galaxy in its
image-plane. Different physical regions, 5 to 7 kpc apart within the galaxy,
drive the outflows at different velocities ( to km
s), and mass outflow rates ( 183 to 527 $M_{\odot}\
yr^{-1}^{-1}^2^2
\sim -120-242^{-1}\simM_{\odot}\ yr^{-1}\geq\approx$ 10% of the total energy flux
provided by star-formation. These estimates suggest that the outflow in RCS0327
is energy driven. This work shows the importance of small scale variations of
outflow properties due to the variations of local stellar properties of the
host galaxy in the context of galaxy evolution.Comment: 24 pages, 15 figures, 6 tables, submitted to MNRA
Gas Accretion via Lyman Limit Systems
In cosmological simulations, a large fraction of the partial Lyman limit
systems (pLLSs; 16<log N(HI)<17.2) and LLSs (17.2log N(HI)<19) probes
large-scale flows in and out of galaxies through their circumgalactic medium
(CGM). The overall low metallicity of the cold gaseous streams feeding galaxies
seen in these simulations is the key to differentiating them from metal rich
gas that is either outflowing or being recycled. In recent years, several
groups have empirically determined an entirely new wealth of information on the
pLLSs and LLSs over a wide range of redshifts. A major focus of the recent
research has been to empirically determine the metallicity distribution of the
gas probed by pLLSs and LLSs in sizable and representative samples at both low
(z2) redshifts. Here I discuss unambiguous evidence for
metal-poor gas at all z probed by the pLLSs and LLSs. At z<1, all the pLLSs and
LLSs so far studied are located in the CGM of galaxies with projected distances
<100-200 kpc. Regardless of the exact origin of the low-metallicity pLLSs/LLSs,
there is a significant mass of cool, dense, low-metallicity gas in the CGM that
may be available as fuel for continuing star formation in galaxies over cosmic
time. As such, the metal-poor pLLSs and LLSs are currently among the best
observational evidence of cold, metal-poor gas accretion onto galaxies.Comment: Invited review to appear in Gas Accretion onto Galaxies, Astrophysics
and Space Science Library, eds. A. J. Fox & R. Dav\'e, to be published by
Springe
Gas Accretion in Star-Forming Galaxies
Cold-mode gas accretion onto galaxies is a direct prediction of LCDM
simulations and provides galaxies with fuel that allows them to continue to
form stars over the lifetime of the Universe. Given its dramatic influence on a
galaxy's gas reservoir, gas accretion has to be largely responsible for how
galaxies form and evolve. Therefore, given the importance of gas accretion, it
is necessary to observe and quantify how these gas flows affect galaxy
evolution. However, observational data have yet to conclusively show that gas
accretion ubiquitously occurs at any epoch. Directly detecting gas accretion is
a challenging endeavor and we now have obtained a significant amount of
observational evidence to support it. This chapter reviews the current
observational evidence of gas accretion onto star-forming galaxies.Comment: Invited review to appear in Gas Accretion onto Galaxies, Astrophysics
and Space Science Library, eds. A. J. Fox & R. Dav\'e, to be published by
Springer. This chapter includes 22 pages with 7 Figure
Observational Diagnostics of Gas Flows: Insights from Cosmological Simulations
Galactic accretion interacts in complex ways with gaseous halos, including
galactic winds. As a result, observational diagnostics typically probe a range
of intertwined physical phenomena. Because of this complexity, cosmological
hydrodynamic simulations have played a key role in developing observational
diagnostics of galactic accretion. In this chapter, we review the status of
different observational diagnostics of circumgalactic gas flows, in both
absorption (galaxy pair and down-the-barrel observations in neutral hydrogen
and metals; kinematic and azimuthal angle diagnostics; the cosmological column
density distribution; and metallicity) and emission (Lya; UV metal lines; and
diffuse X-rays). We conclude that there is no simple and robust way to identify
galactic accretion in individual measurements. Rather, progress in testing
galactic accretion models is likely to come from systematic, statistical
comparisons of simulation predictions with observations. We discuss specific
areas where progress is likely to be particularly fruitful over the next few
years.Comment: Invited review to appear in Gas Accretion onto Galaxies, Astrophysics
and Space Science Library, eds. A. J. Fox & R. Dave, to be published by
Springer. Typos correcte
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