We present the first high-resolution map of the cold molecular gas distribution as traced by CO(2−1) emission with ALMA in a long ram pressure stripped tail. The Norma cluster galaxy ESO 137-001 is ...undergoing a strong interaction with the surrounding intracluster medium and is one of the nearest jellyfish galaxies with a long multiphase and multicomponent tail. We have mapped the full extent of the tail at 1″ (350 pc) angular resolution and found a rich distribution of mostly compact CO regions extending to nearly 60 kpc in length and 25 kpc in width. In total, about 109 M of molecular gas was detected with ALMA. From comparison with previous APEX observations, we also infer the presence of a substantial extended molecular component in the tail. The ALMA CO features are found predominantly at the heads of numerous small-scale (∼1.5 kpc) fireballs (i.e., star-forming clouds with linear streams of young stars extending toward the galaxy) but also large-scale (∼8 kpc) superfireballs and double-sided fireballs that have additional diffuse ionized gas tails extending in the direction opposite the stellar tails. The new data help to shed light on the origin of the molecular tail; CO filaments oriented in the direction of the tail are likely young molecular features formed in situ, whereas large CO features tilted with respect to the tail may have originated from dense gas complexes that were gradually pushed away from the disk.
We present a new survey of HCN(1-0) emission, a tracer of dense molecular gas, focused on the little-explored regime of normal star-forming galaxy disks. Combining HCN, CO, and infrared (IR) ...emission, we investigate the role of dense gas in star formation, finding systematic variations in both the apparent dense gas fraction (traced by the HCN-to-CO ratio) and the apparent star formation efficiency of dense gas. The latter may be unexpected, given the recent popularity of gas density threshold models to explain star formation scaling relations. Our survey used the IRAM 30 m telescope to observe HCN(1-0), CO(1-0), and several other emission lines across 29 nearby disk galaxies whose CO(2-1) emission has previously been mapped by the HERACLES survey. We detected HCN in 48 out of 62 observed positions. We explore one such model in which variations in the Mach number drive many of the trends within galaxy disks, while density contrasts drive the differences between disk and merging galaxies.
ABSTRACT
Previous studies have revealed a population of galaxies in galaxy clusters with ram pressure stripped (RPS) tails of gas and embedded young stars. We observed 1.4 GHz continuum and H i ...emission with the Very Large Array in its B-configuration in two fields of the Coma cluster to study the radio properties of RPS galaxies. The best continuum sensitivities in the two fields are 6 and 8 µJy per 4 arcsec beam, respectively, which are 4 and 3 times deeper than those previously published. Radio continuum tails are found in 10 (8 are new) out of 20 RPS galaxies, unambiguously revealing the presence of relativistic electrons and magnetic fields in the stripped tails. Our results also hint that the tail has a steeper spectrum than the galaxy. The 1.4 GHz continuum in the tails is enhanced relative to their H α emission by a factor of ∼7 compared to the main bodies of the RPS galaxies. The 1.4 GHz continuum of the RPS galaxies is also enhanced relative to their infrared emission by a factor of ∼2 compared to star-forming galaxies. The enhancement is likely related to ram pressure and turbulence in the tail. We furthermore present H i detections in three RPS galaxies and upper limits for the other RPS galaxies. The cold gas in D100’s stripped tail is dominated by molecular gas, which is likely a consequence of the high ambient pressure. No evidence of radio emission associated with ultra-diffuse galaxies is found in our data.
We present a study of the spatially resolved radio continuum-star formation rate (RC-SFR) relation using state-of-the-art star formation tracers in a sample of 17 THINGS galaxies. We use SFR surface ...density ( capital sigma sub(sfr)) maps created by a linear combination of GALEX far-UV (FUV) and Spitzer 24 mu m maps. We find a tight correlation between the radial profiles of the radio and FUV/MIR-based capital sigma sub(sfr) for the entire extent of the disk. The ratio R of the azimuthally averaged radio to FUV/MIR-based capital sigma sub(sfr) agrees with the integrated ratio and has only quasi-random fluctuations with galactocentric radius that are relatively small. We studied the ratio R of radio to FUV/MIR-based integrated SFR as a function of global galaxy parameters and found no clear correlation. We can reconcile our finding of an almost linear RC-S FR relation and sub-linear resolved RC- capital sigma sub(sfr) relation by proposing a non-linear magnetic field-SFR relation, B is proportional to SFR super(0.30 + or - 0.02) sub(hyb), which holds both globally and locally.
We make a direct comparison of the derived dark matter (DM) distributions between hydrodynamical simulations of dwarf galaxies assuming a Delta *LCDM cosmology and the observed dwarf galaxies sample ...from the THINGS survey in terms of (1) the rotation curve shape and (2) the logarithmic inner density slope Delta *a of mass density profiles. The simulations, which include the effect of baryonic feedback processes, such as gas cooling, star formation, cosmic UV background heating, and most importantly, physically motivated gas outflows driven by supernovae, form bulgeless galaxies with DM cores. We show that the stellar and baryonic mass is similar to that inferred from photometric and kinematic methods for galaxies of similar circular velocity. Analyzing the simulations in exactly the same way as the observational sample allows us to address directly the so-called cusp/core problem in the Delta *LCDM model. We show that the rotation curves of the simulated dwarf galaxies rise less steeply than cold dark matter rotation curves and are consistent with those of the THINGS dwarf galaxies. The mean value of the logarithmic inner density slopes Delta *a of the simulated galaxies' DM density profiles is ~--0.4 ? 0.1, which shows good agreement with Delta *a = --0.29 ? 0.07 of the THINGS dwarf galaxies. The effect of non-circular motions is not significant enough to affect the results. This confirms that the baryonic feedback processes included in the simulations are efficiently able to make the initial cusps with Delta *a ~--1.0 to --1.5 predicted by DM-only simulations shallower and induce DM halos with a central mass distribution similar to that observed in nearby dwarf galaxies.
Galaxy interactions are often accompanied by an enhanced star formation rate (SFR). Since molecular gas is essential for star formation, it is vital to establish whether and by how much galaxy ...interactions affect the molecular gas properties. We investigate the effect of interactions on global molecular gas properties by studying a sample of 58 galaxies in pairs and 154 control galaxies. Molecular gas properties are determined from observations with the JCMT, PMO, and CSO telescopes and supplemented with data from the xCOLD GASS and JINGLE surveys at 12CO(1-0) and 12CO(2-1). The SFR, gas mass ( ), and gas fraction (fgas) are all enhanced in galaxies in pairs by ∼2.5 times compared to the controls matched in redshift, mass, and effective radius, while the enhancement of star formation efficiency (SFE SFR/ ) is less than a factor of 2. We also find that the enhancements in SFR, and fgas, increase with decreasing pair separation and are larger in systems with smaller stellar mass ratio. Conversely, the SFE is only enhanced in close pairs (separation <20 kpc) and equal-mass systems; therefore, most galaxies in pairs lie in the same parameter space on the SFR- plane as controls. This is the first time that the dependence of molecular gas properties on merger configurations is probed statistically with a relatively large sample and a carefully selected control sample for individual galaxies. We conclude that galaxy interactions do modify the molecular gas properties, although the strength of the effect is dependent on merger configuration.
[C i](1–0) and [C i](2–1) in Resolved Local Galaxies Crocker, Alison F.; Pellegrini, Eric; Smith, J.-D. T. ...
Astrophysical journal/The Astrophysical journal,
12/2019, Volume:
887, Issue:
1
Journal Article
Peer reviewed
Open access
Abstract
We present resolved C
i
line intensities of 18 nearby galaxies observed with the SPIRE FTS spectrometer on the
Herschel Space Observatory
. We use these data along with resolved CO line ...intensities from
J
up
= 1 to 7 to interpret what phase of the interstellar medium the C
i
lines trace within typical local galaxies. A tight, linear relation is found between the intensities of the CO(4–3) and C
i
(2–1) lines; we hypothesize this is due to the similar upper level temperature of these two lines. We modeled the C
i
and CO line emission using large-velocity gradient models combined with an empirical template. According to this modeling, the C
i
(1–0) line is clearly dominated by the low-excitation component. We determine C
i
to molecular mass conversion factors for both the C
i
(1–0) and C
i
(2–1) lines, with mean values of
α
C
i
(1−0)
= 7.3
M
⊙
K
−1
km
−1
s pc
−2
and
α
C
i
(2−1)
= 34
M
⊙
K
−1
km
−1
s pc
−2
with logarithmic root-mean-square spreads of 0.20 and 0.32 dex, respectively. The similar spread of
to
(derived using the CO(2–1) line) suggests that C
i
(1–0) may be just as good a tracer of cold molecular gas as CO(2–1) in galaxies of this type. On the other hand, the wider spread of
α
C
i
(2−1)
and the tight relation found between C
i
(2–1) and CO(4–3) suggest that much of the C
i
(2–1) emission may originate in warmer molecular gas.
In this paper, we examine to what extent the radio continuum can be used as an extinction-free probe of star formation in dwarf galaxies. To that aim, we observe 40 nearby dwarf galaxies with the ...Very Large Array at 6 cm (4-8 GHz) in C-configuration. We obtained images with 3″-8″ resolution and noise levels of 3-15 Jy beam−1. We detected emission associated with 22 of the 40 dwarf galaxies, eight of which are new detections. The general picture is that of an interstellar medium largely devoid of radio continuum emission, interspersed by isolated pockets of emission associated with star formation. We find an average thermal fraction of ∼50%-70% and an average magnetic field strength of ∼5-8 G, only slightly lower than that found in larger, spiral galaxies. At 100 pc scales, we find surprisingly high values for the average magnetic field strength of up to 50 G. We find that dwarf galaxies follow the theoretical predictions of the radio continuum-star formation rate relation within regions of significant radio continuum emission but that the nonthermal radio continuum is suppressed relative to the star formation rate when considering the entire optical disk. We examine the far-infrared-star formation rate relation for our sample and find that the far-infrared is suppressed compared to the expected star formation rate. We discuss explanations for these observed relations and the impact of our findings on the radio continuum-far-infrared relation. We conclude that radio continuum emission at centimeter wavelengths has the promise of being a largely extinction-free star formation rate indicator. We find that star formation rates of gas-rich, low-mass galaxies can be estimated with an uncertainty of 0.2 dex between the values of 2 × 10−4 and 0.1 M yr−1.
Atacama Large Millimeter Array (ALMA) observations of CO(1-0) emission in the interacting galaxies IC 2163 and NGC 2207 are used to determine the properties of molecular clouds and their association ...with star-forming regions observed with the Hubble Space Telescope. Half of the CO mass is in 249 clouds, each more massive than . The mass distribution functions for the CO clouds and star complexes in a galactic-scale shock front in IC 2163 both have a slope on a log-log plot of −0.7, similar to what is observed in Milky Way clouds. The molecular cloud mass function is steeper in NGC 2207. The CO distribution in NGC 2207 also includes a nuclear ring, a mini-bar, and a mini-starburst region that dominates the , radio, and H emission in both galaxies. The ratio of the sum of the masses of star complexes younger than 30 Myr to the associated molecular cloud masses is ∼4%. The maximum age of star complexes in the galactic-scale shock front in IC 2163 is about 200 Myr, the same as the interaction time of the two galaxies, suggesting the destruction of older complexes in the eyelids.
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