اشترك بالحزمة الذهبية واحصل على وصول غير محدود شمرا أكاديميا
تسجيل مستخدم جديدDust continuum emission as a tracer of gas mass in galaxies
179
0
0.0
(
0
)
اسأل ChatGPT حول البحث
ﻻ يوجد ملخص باللغة العربية
We use a sample of 36 galaxies from the KINGFISH (Herschel IR), HERACLES (IRAM CO), and THINGS (VLA HI) surveys to study empirical relations between Herschel infrared (IR) luminosities and the total mass of the interstellar gas (H2+HI). Such a comparison provides a simple empirical relationship without introducing the uncertainty of dust model fitting. We find tight correlations, and provide fits to these relations, between Herschel luminosities and the total gas mass integrated over entire galaxies, with the tightest, almost linear, correlation found for the longest wavelength data (SPIRE500). However, we find that accounting for the gas-phase metallicity (affecting the dust-to-gas ratio) is crucial when applying these relations to low-mass, and presumably high-redshift, galaxies. The molecular (H2) gas mass is found to be better correlated with the peak of the IR emission (e.g. PACS160), driven mostly by the correlation of stellar mass and mean dust temperature. When examining these relations as a function of galactocentric radius we find the same correlations, albeit with a larger scatter, up to a radius of 0.7 r_25 (within which most of the galaxys baryonic mass resides). However, beyond this radius the same correlations no longer hold, with the gas mass (predominantly HI) increasing relative to the infrared emission. The tight relations found for the bulk of the galaxys baryonic content suggest that the total gas masses of disk-like (non-merging) galaxies can be inferred from far-infrared continuum measurements in situations where only the latter are available, e.g. in ALMA continuum observations of high-redshift galaxies.
قيم البحث
اقرأ أيضاً
Trends observed in galaxies, such as the Gao & Solomon relation, suggest a linear relation between the star formation rate and the mass of dense gas available for star formation. Validation of such relations requires the establishment of reliable met
hods to trace the dense gas in galaxies. One frequent assumption is that the HCN ($J=1$--0) transition is unambiguously associated with gas at $rm{}H_2$ densities $gg{}10^4~rm{}cm^{-3}$. If so, the mass of gas at densities $gg{}10^4~rm{}cm^{-3}$ could be inferred from the luminosity of this emission line, $L_{rm{}HCN,(1text{--}0)}$. Here we use observations of the Orion~A molecular cloud to show that the HCN ($J=1$--0) line traces much lower densities $sim{}10^3~rm{}cm^{-3}$ in cold sections of this molecular cloud, corresponding to visual extinctions $A_Vapprox{}6~rm{}mag$. We also find that cold and dense gas in a cloud like Orion produces too little HCN emission to explain $L_{rm{}HCN,(1text{--}0)}$ in star--forming galaxies, suggesting that galaxies might contain a hitherto unknown source of HCN emission. In our sample of molecules observed at frequencies near 100~GHz (also including $rm{}^{12}CO$, $rm{}^{13}CO$, $rm{}C^{18}O$, CN, and CCH), $rm{}N_2H^+$ is the only species clearly associated with rather dense gas.
It has been recently argued that the HCN J=1--0 line emission may not be an unbiased tracer of dense molecular gas ($rm nga 10^4 cm^{-3}$) in Luminous Infrared Galaxies (LIRGs: $rm L_{FIR}> 10^{11} L_{odot}$) and HCO$^+$ J=1--0 may constitute a bette
r tracer instead (Gracia-Carpio et al. 2006), casting doubt into earlier claims supporting the former as a good tracer of such gas (Gao & Solomon 2004; Wu et al. 2006). In this paper new sensitive HCN J=4--3 observations of four such galaxies are presented, revealing a surprisingly wide excitation range for their dense gas phase that may render the J=1--0 transition from either species a poor proxy of its mass. Moreover the well-known sensitivity of the HCO$^+$ abundance on the ionization degree of the molecular gas (an important issue omitted from the ongoing discussion about the relative merits of HCN and HCO$^+$ as dense gas tracers) may severely reduce the HCO$^+$ abundance in the star-forming and highly turbulent molecular gas found in LIRGs, while HCN remains abundant. This may result to the decreasing HCO$^+$/HCN J=1--0 line ratio with increasing IR luminosity found in LIRGs, and casts doubts on the HCO$^+$ rather than the HCN as a good dense molecular gas tracer. Multi-transition observations of both molecules are needed to identify the best such tracer, its relation to ongoing star formation, and constrain what may be a considerable range of dense gas properties in such galaxies.
We investigate the evolution of the gas mass fraction for galaxies in the COSMOS field using submillimetre emission from dust at 850$mu$m. We use stacking methodologies on the 850$mu$m S2COSMOS map to derive the gas mass fraction of galaxies out to h
igh redshifts, 0 <= $z$ <= 5, for galaxies with stellar masses of $10^{9.5} < M_* (rm M_{odot}) < 10^{11.75}$. In comparison to previous literature studies we extend to higher redshifts, include more normal star-forming galaxies (on the main sequence), and also investigate the evolution of the gas mass fraction split by star-forming and passive galaxy populations. We find our stacking results broadly agree with scaling relations in the literature. We find tentative evidence for a peak in the gas mass fraction of galaxies at around $z$ ~ 2.5-3, just before the peak of the star formation history of the Universe. We find that passive galaxies are particularly devoid of gas, compared to the star-forming population. We find that even at high redshifts, high stellar mass galaxies still contain significant amounts of gas.
Though half of cosmic starlight is absorbed by dust and reradiated at long wavelengths (3$mu$m-3mm), constraints on the infrared through millimeter galaxy luminosity function (the `IRLF) are poor in comparison to the rest-frame ultraviolet and optica
l galaxy luminosity function, particularly at z>2.5. Here we present a backward evolution model for interpreting number counts, redshift distributions, and cross-band flux density correlations in the infrared and submillimeter sky, from 70$mu$m-2mm, using a model for the IRLF out to the epoch of reionization. Mock submillimeter maps are generated by injecting sources according to the prescribed IRLF and flux densities drawn from model spectral energy distributions that mirror the distribution of SEDs observed in $0<z<5$ dusty star-forming galaxies (DSFGs). We explore two extreme hypothetical case-studies: a dust-poor early Universe model, where DSFGs contribute negligibly ($<$10%) to the integrated star-formation rate density at $z>4$, and an alternate dust-rich early Universe model, where DSFGs dominate $sim$90% of $z>4$ star-formation. We find that current submm/mm datasets do not clearly rule out either of these extreme models. We suggest that future surveys at 2mm will be crucial to measuring the IRLF beyond $zsim4$. The model framework developed in this paper serves as a unique tool for the interpretation of multiwavelength IR/submm extragalactic datasets and will enable more refined constraints on the IRLF than can be made from direct measurements of individual galaxies integrated dust emission.
The [CII] 157.74 $mu$m transition is the dominant coolant of the neutral interstellar gas, and has great potential as a star formation rate (SFR) tracer. Using the Herschel KINGFISH sample of 46 nearby galaxies, we investigate the relation of [CII] s
urface brightness and luminosity with SFR. We conclude that [CII] can be used for measurements of SFR on both global and kiloparsec scales in normal star-forming galaxies in the absence of strong active galactic nuclei (AGN). The uncertainty of the $Sigma_{rm [CII]}-Sigma_{rm SFR}$ calibration is $pm$0.21 dex. The main source of scatter in the correlation is associated with regions that exhibit warm IR colors, and we provide an adjustment based on IR color that reduces the scatter. We show that the color-adjusted $Sigma_{rm[CII]}-Sigma_{rm SFR}$ correlation is valid over almost 5 orders of magnitude in $Sigma_{rm SFR}$, holding for both normal star-forming galaxies and non-AGN luminous infrared galaxies. Using [CII] luminosity instead of surface brightness to estimate SFR suffers from worse systematics, frequently underpredicting SFR in luminous infrared galaxies even after IR color adjustment (although this depends on the SFR measure employed). We suspect that surface brightness relations are better behaved than the luminosity relations because the former are more closely related to the local far-UV field strength, most likely the main parameter controlling the efficiency of the conversion of far-UV radiation into gas heating. A simple model based on Starburst99 population-synthesis code to connect SFR to [CII] finds that heating efficiencies are $1%-3%$ in normal galaxies.
سجل دخول لتتمكن من نشر تعليقات
التعليقات
جاري جلب التعليقات
سجل دخول لتتمكن من متابعة معايير البحث التي قمت باختيارها
