17 research outputs found
Gas Loss by Ram Pressure Stripping and Internal Feedback From Low Mass Milky Way Satellites
The evolution of dwarf satellites of the Milky Way is affected by the
combination of ram pressure and tidal stripping, and internal feedback from
massive stars. We investigate gas loss processes in the smallest satellites of
the Milky Way using three-dimensional, high resolution, idealized wind tunnel
simulations, accounting for gas loss through both ram pressure stripping and
expulsion by supernova feedback. Using initial conditions appropriate for a
dwarf galaxy like Leo T, we investigate whether or not environmental gas
stripping and internal feedback can quench these low mass galaxies on the
expected timescales, shorter than 2 Gyr. We find that supernova feedback
contributes negligibly to the stripping rate for these low star formation rate
galaxies. However, we also find that ram pressure stripping is less efficient
than expected in the stripping scenarios we consider. Our work suggests that,
although ram pressure stripping can eventually completely strip these galaxies,
other physics is likely at play to reconcile our computed stripping times with
the rapid quenching timescales deduced from observations of low mass Milky Way
dwarf galaxies. We discuss the roles additional physics may play in this
scenario, including host-satellite tidal interactions, cored vs. cuspy dark
matter profiles, reionization, and satellite pre-processing. We conclude that a
proper accounting of these physics together is necessary to understand the
quenching of low mass Milky Way satellites.Comment: 16 pages, 7 figures. Accepted for publication in Ap
The GALFA-HI Survey: Data Release 1
We present the Galactic Arecibo L-Band Feed Array HI (GALFA-HI) survey, and
its first full data release (DR1). GALFA-HI is a high resolution (~ 4'), large
area (13000 deg^2), high spectral resolution (0.18 km/s), wide band (-700 <
v_LSR < +700 km/s) survey of the Galactic interstellar medium in the 21-cm line
hyperfine transition of neutral hydrogen conducted at Arecibo Observatory.
Typical noise levels are 80 mK RMS in an integrated 1 km/s channel. GALFA-HI is
a dramatic step forward in high-resolution, large-area Galactic HI surveys, and
we compare GALFA-HI to past, present, and future Galactic HI surveys. We
describe in detail new techniques we have developed to reduce these data in the
presence of fixed pattern noise, gain variation, and inconsistent beam shapes,
and we show how we have largely mitigated these effects. We present our first
full data release, covering 7520 square degrees of sky and representing 3046
hours of integration time, and discuss the details of these data.Comment: Accepted to the ApJ
Compact HI clouds from the GALFA-HI survey
The Galactic Arecibo L-band Feed Array HI (GALFA-HI) survey is mapping the
entire Arecibo sky at 21-cm, over a velocity range of -700 to +700 km/s (LSR),
at a velocity resolution of 0.18 km/s and a spatial resolution of 3.5 arcmin.
The unprecedented resolution and sensitivity of the GALFA-HI survey have
resulted in the detection of numerous isolated, very compact HI clouds at low
Galactic velocities, which are distinctly separated from the HI disk emission.
In the limited area of ~4600 deg surveyed so far, we have detected 96 of
such compact clouds. The detected clouds are cold with a median T
(the kinetic temperature in the case in which there is no non-thermal
broadening) of 300 K. Moreover, these clouds are quite compact and faint, with
median values of 5 arcmin in angular size, 0.75 K in peak brightness
temperature, and cm in HI column density. Most of the
clouds deviate from Galactic rotation at the 20-30 km/s level, and a
significant fraction show evidence for a multiphase medium and velocity
gradients. No counterparts for these clouds were found in other wavebands. From
the modeling of spatial and velocity distributions of the whole compact cloud
population, we find that the bulk of the compact clouds are related to the
Galactic disk, and their distances are likely to be in the range of 0.1 to a
few kpc. We discuss various possible scenarios for the formation and
maintenance of this cloud population and its significance for Galactic ISM
studies.Comment: Accepted for publication in the Astrophysical Journa
Modeling the Physical Structure of the Low Density Pre-protostellar Core Lynds 1498
Lynds 1498 is a pre-protostellar core (PPC) and was one of the initial
objects toward which molecular depletion and differentiation was detected.
Despite the considerable scrutiny of L1498, there has not been a extensive
study of the density and temperature structure as derived from radiative
transfer modeling of dust continuum observations. We present deep SCUBA
observations of L1498 at 850 and 450 micron, high resolution BEARS maps of the
N2H+ 1-0 transition, CSO observations of the N2H+ 3-2 transition, and GBT
observations of the C3S 4-3 transition. We also present a comparison of derived
properties between L1498 and nearby PPCs that have been observed at
far-infrared and submillimeter wavelengths. We present a more realistic
treatment of PPC heating which varies the strength of the ISRF, Sisrf, and
includes attenuation of the ISRF due to dust grains at the outer radius of the
core, Av. The best-fitted model consists of a Bonner-Ebert sphere with a
central density of 1 - 3 x 10^4 cm-3, R_o ~ 0.29 pc, 0.5 <= Sisrf <= 1, Av ~ 1
mag, and a nearly isothermal temperature profile of ~ 10.5 K for OH8 opacities.
C3S emission shows a central depletion hole while N2H+ emission is centrally
peaked. The observed depletions of C3S and H2CO, the modest N2H+ abundance, and
a central density that is an order of magnitude lower than other modeled PPCs
suggests that L1498 may be a forming PPC. Our derived temperature and density
profile will improve modeling of molecular line observations that will
explicate the core's kinematical and chemical state. (abridged)Comment: 26 pages, 10 figures (2 color figs). Accepted to Ap