403 research outputs found
CI emission in Ultra Luminous Infrared Galaxies as a molecular gas mass tracer
We present new sensitive wide-band measurements of the fine structure line
3^P_1 -> 3^P_0 (J=1-0, 492GHz) of neutral atomic carbon (CI) in the two typical
Ultra Luminous Infrared Galaxies NGC6240 and Arp220. We then use them along
with several other CI measurements in similar objects found in the literature
to estimate their global molecular gas content under the assumption of a full
CI-H_2 concomitance. We find excellent agreement between the H_2 gas mass
estimated with this method and the standard methods using 12^CO. This may
provide a new way to measure H_2 gas mass in galaxies, and one which may be
very valuable in ULIRGs since in such systems the bright 12^CO emission is
known to systematically overestimate the gas mass while their 13^CO emission is
usually very weak. At redshifts z>=1 the CI J=1-0 line shifts to much more
favorable atmospheric windows and can become a viable alternative tracer of the
H_2 gas fueling starburst events in the distant Universe.Comment: 11 pages, 2 figures. Accepted for publication in ApJ Letter
SImulator of GAlaxy Millimetre/submillimetre Emission (SIGAME): CO emission from massive z=2 main-sequence galaxies
We present SIGAME (SImulator of GAlaxy Millimetre/submillimetre Emission), a
new numerical code designed to simulate the 12CO rotational line emission
spectrum of galaxies. Using sub-grid physics recipes to post-process the
outputs of smoothed particle hydrodynamics (SPH) simulations, a molecular gas
phase is condensed out of the hot and partly ionized SPH gas. The gas is
subjected to far-UV radiation fields and cosmic ray ionization rates which are
set to scale with the local star formation rate volume density. Level
populations and radiative transport of the CO lines are solved with the 3-D
radiative transfer code LIME. We have applied SIGAME to cosmological SPH
simulations of three disc galaxies at z=2 with stellar masses in the range
~(0.5-2)x10^11 Msun and star formation rates ~40-140 Msun/yr. Global CO
luminosities and line ratios are in agreement with observations of disc
galaxies at z~2 up to and including J=3-2 but falling short of the few existing
J=5-4 observations. The central 5 kpc regions of our galaxies have CO 3-2/1-0
and 7-6/1-0 brightness temperature ratios of ~0.55-0.65 and ~0.02-0.08,
respectively, while further out in the disc the ratios drop to more quiescent
values of ~0.5 and <0.01. Global CO-to-H2 conversion (alpha_CO) factors are
~=1.5 Msun*pc^2/(K km s/1), i.e. ~2-3 times below typically adopted values for
disc galaxies, and alpha_CO increases with radius, in agreement with
observations of nearby galaxies. Adopting a top-heavy Giant Molecular Cloud
(GMC) mass spectrum does not significantly change the results. Steepening the
GMC density profile leads to higher global line ratios for J_up>=3 and CO-to-H2
conversion factors [~=3.6 Msun*pc^2/(K km/s)].Comment: 28 pages, 20 figures. Accepted for Publication in MNRAS. Substantial
revisions from the previous version, including tests with model galaxies
similar to the Milky Way. Improved figures and added table
Origins of the extragalactic background at 1mm from a combined analysis of the AzTEC and MAMBO data in GOODS-N
We present a study of the cosmic infrared background, which is a measure of
the dust obscured activity in all galaxies in the Universe. We venture to
isolate the galaxies responsible for the background at 1mm; with spectroscopic
and photometric redshifts we constrain the redshift distribution of these
galaxies. We create a deep 1.16mm map (sigma ~ 0.5mJy) by combining the AzTEC
1.1mm and MAMBO 1.2mm datasets in GOODS-N. This combined map contains 41 secure
detections, 13 of which are new. By averaging the 1.16mm flux densities of
individually undetected galaxies with 24um flux densities > 25uJy, we resolve
31--45 per cent of the 1.16mm background. Repeating our analysis on the SCUBA
850um map, we resolve a higher percentage (40--64 per cent) of the 850um
background. A majority of the background resolved (attributed to individual
galaxies) at both wavelengths comes from galaxies at z > 1.3. If the ratio of
the resolved submillimeter to millimeter background is applied to a reasonable
scenario for the origins of the unresolved submillimeter background, 60--88 per
cent of the total 1.16mm background comes from galaxies at z > 1.3.Comment: 12 pages, 10 figures. Accepted by MNRAS. The combined map is publicly
available at http://www.astro.umass.edu/~pope/goodsn_mm
A 1200-μm MAMBO survey of the GOODS-N field: a significant population of submillimetre dropout galaxies
We present a 1200-mu m image of the Great Observatories Origin Deep Survey North (GOODS-N) field, obtained with the Max Planck Millimetre Bolometer array (MAMBO) on the IRAM 30-m telescope. The survey covers a contiguous area of 287 arcmin(^2) to a near-uniform noise level of similar to 0.7mJy beam(^-1). After Bayesian flux deboosting, a total of 30 sources are recovered (>= 3.5 sigma). An optimal combination of our 1200-mu m data and an existing 850-mu m image from the Submillimetre Common-User Bolometer Array (SCUBA) yielded 33 sources (>= 4 sigma). We combine our GOODS-N sample with those obtained in the Lockman Hole and ELAIS N2 fields (Scott et al. 2002; Greve et al. 2004) in order to explore the degree of overlap between 1200-and 850-mu m-selected galaxies (hereafter SMGs), finding no significant difference between their S-850 mu m/S-1200 mu m distributions. However, a noise-weighted stacking analysis yields a significant detection of the 1200-mu m-blank SCUBA sources, S-850 mu m/S-1200 mu m = 3.8 +/- 0.4, whereas no significant 850-mu m signal is found for the 850-mu m-blank MAMBO sources (S-850 mu m/S-1200 mu m = 0.7 +/- 0.3). The hypothesis that the S-850 mu m/S-1200 mu m distribution of SCUBA sources is also representative of the MAMBO population is rejected at the similar to 4 sigma level, via Monte Carlo simulations. Therefore, although the populations overlap, galaxies selected at 850 and 1200 mu m are different, and there is compelling evidence for a significant 1200-mu m-detected population which is not recovered at 850 mu m. These are submillimetre dropouts (SDOs), with S-850 mu m/S-1200 mu m = 0.7-1.7, requiring very cold dust or unusual spectral energy distributions (T-d similar or equal to 10 K; beta similar or equal to 1), unless SDOs reside beyond the redshift range observed for radio-identified SMGs, i. e. at z > 4
Investigating the [C]-to-H conversion factor and the H gas budget of galaxies at with hydrodynamical simulations
One of the most fundamental baryonic matter components of galaxies is the
neutral atomic hydrogen (H). At low redshifts, this
component can be traced directly through the 21-cm transition, but to infer
H gas content of the most distant galaxies, a viable
tracer is needed. We here investigate the fidelity of the fine structure
transition of the () transition of singly-ionized carbon
[C] at m as a proxy for H in a set simulated galaxies at , following the work by Heintz
et al. (2021). We select 11,125 star-forming galaxies from the SIMBA
simulations, with far-infrared line emissions post-processed and modeled within
the SIGAME framework. We find a strong connection between [C] and H, with the relation between this [C]-to-H relation () being anti-correlated with the gas-phase metallicity of the
simulated galaxies. We further use these simulations to make predictions for
the total baryonic matter content of galaxies at , and specifically
the HI gas mass fraction. We find mean values of ,
and . These results provide strong evidence
for H being the dominant baryonic matter component by
mass in galaxies at .Comment: 7 pages, 3 figures. Accepted for publication by ApJ
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