Search for: All records

Abstract We present a catalog of clouds identified from the¹²CO (1–0) data of M83, which was observed using the Atacama Large Millimeter/submillimeter Array with a spatial resolution of ∼46 pc and a mass sensitivity of ∼10⁴M_⊙(3σ). The almost full-disk coverage and high sensitivity of the data allowed us to sample 5724 molecular clouds with a median mass of ∼1.9 × 10⁵M_⊙, which is comparable to the most frequently sampled mass of giant molecular clouds by surveys in the Milky Way (MW). About 60% of the total CO luminosity in M83's disk arises from clouds more massive than 10⁶M_⊙. Such massive clouds comprise 16% of the total clouds in number and tend to concentrate toward the arm, bar, and center, while smaller clouds are more prevalent in interarm regions. Most >10⁶M_⊙clouds have peak brightness temperaturesT_peakabove 2 K with the current resolution. Comparing the observed cloud properties with the scaling relations determined by P. M. Solomon et al. (1987, hereafter S87),T_peak> 2 K clouds follow the relations, butT_peak< 2 K clouds, which are dominant in number, deviate significantly. Without considering the effect of beam dilution, the deviations would suggest modestly high virial parameters (medianα_vir∼ 2.7) and low surface mass densities (median Σ ∼ 22M_⊙pc⁻²) for the entire cloud samples, which are similar to values found for the MW clouds by T. S. Rice et al. (2016) and M.-A Miville-Deschênes et al. (2017). However, once beam dilution is taken into account, the observedα_virand Σ for a majority of the clouds (mostlyT_peak<2 K) can be potentially explained with intrinsic Σ of ∼100M_⊙pc⁻²andα_virof ∼1, which are similar to the clouds of S87. 

Abstract The spatial range for feedback from star formation varies from molecular cloud disruption on parsec scales to supershells and disk blowout on kiloparsec scales. The relative amounts of energy and momentum given to these scales are important for understanding the termination of star formation in any one region and the origin of interstellar turbulence and disk stability in galaxies as a whole. Here, we measure, for 11 THINGS galaxies, the excess kinetic energy, velocity dispersion, and surface density of H i gas associated with regions of excess star formation, where the excess is determined from the difference between the observed local value and the azimuthal average. We find small decreases in the excess kinetic energy and velocity dispersion in regions of excess star formation rate density, suggesting that most of the feedback energy does not go into local H i motion. Most likely, it disrupts molecular clouds and dissipates rapidly at high gas density. Some could also be distributed over larger regions, filling in spaces between the peaks of star formation and contributing to other energy sources from self-gravity and spiral arm shocks. 

Abstract We present Atacama Large Millimeter/submillimeter Array (ALMA) imaging of molecular gas across the full star-forming disk of the barred spiral galaxy M83 in CO( J = 1–0). We jointly deconvolve the data from ALMA’s 12 m, 7 m, and Total Power arrays using the MIRIAD package. The data have a mass sensitivity and resolution of 10 4 M ⊙ (3 σ ) and 40 pc—sufficient to detect and resolve a typical molecular cloud in the Milky Way with a mass and diameter of 4 × 10 5 M ⊙ and 40 pc, respectively. The full disk coverage shows that the characteristics of molecular gas change radially from the center to outer disk, with the locally measured brightness temperature, velocity dispersion, and integrated intensity (surface density) decreasing outward. The molecular gas distribution shows coherent large-scale structures in the inner part, including the central concentration, offset ridges along the bar, and prominent molecular spiral arms. However, while the arms are still present in the outer disk, they appear less spatially coherent, and even flocculent. Massive filamentary gas concentrations are abundant even in the interarm regions. Building up these structures in the interarm regions would require a very long time (≳100 Myr). Instead, they must have formed within stellar spiral arms and been released into the interarm regions. For such structures to survive through the dynamical processes, the lifetimes of these structures and their constituent molecules and molecular clouds must be long (≳100 Myr). These interarm structures host little or no star formation traced by H α . The new map also shows extended CO emission, which likely represents an ensemble of unresolved molecular clouds. 

Abstract The low metallicities of dwarf irregular galaxies (dIrr) greatly influence the formation and structure of molecular clouds. These clouds, which consist primarily of H₂, are typically traced by CO, but low-metallicity galaxies are found to have little CO despite ongoing star formation. In order to probe the conditions necessary for CO core formation in dwarf galaxies, we have used the catalog of Rubio et al. for CO cores in WLM, a Local Group dwarf with an oxygen abundance that is 13% of solar. Here we aim to characterize the galactic environments in which these 57 CO cores formed. We grouped the cores together based on proximity to each other and strong FUV emission, examining properties of the star-forming region enveloping the cores and the surrounding environment where the cores formed. We find that high Hisurface density does not necessarily correspond to higher total CO mass, but regions with higher CO mass have higher Hisurface densities. We also find the cores in star-forming regions spanning a wide range of ages show no correlation between age and CO core mass, suggesting that the small size of the cores is not due to fragmentation of the clouds with age. The presence of CO cores in a variety of different local environments, along with the similar properties between star-forming regions with and without CO cores, leads us to conclude that there are no obvious environmental characteristics that drive the formation of these CO cores. 

ABSTRACT We use the angular two-point correlation function (TPCF) to investigate the hierarchical distribution of young star clusters in 12 local (3–18 Mpc) star-forming galaxies using star cluster catalogs obtained with the Hubble Space Telescope (HST) as part of the Treasury Program Legacy ExtraGalactic UV Survey. The sample spans a range of different morphological types, allowing us to infer how the physical properties of the galaxy affect the spatial distribution of the clusters. We also prepare a range of physically motivated toy models to compare with and interpret the observed features in the TPCFs. We find that, conforming to earlier studies, young clusters ($$T \lesssim 10\, \mathrm{Myr}$$) have power-law TPCFs that are characteristic of fractal distributions with a fractal dimension D2, and this scale-free nature extends out to a maximum scale lcorr beyond which the distribution becomes Poissonian. However, lcorr, and D2 vary significantly across the sample, and are correlated with a number of host galaxy physical properties, suggesting that there are physical differences in the underlying star cluster distributions. We also find that hierarchical structuring weakens with age, evidenced by flatter TPCFs for older clusters ($$T \gtrsim 10\, \mathrm{Myr}$$), that eventually converges to the residual correlation expected from a completely random large-scale radial distribution of clusters in the galaxy in $$\sim 100 \, \mathrm{Myr}$$. Our study demonstrates that the hierarchical distribution of star clusters evolves with age, and is strongly dependent on the properties of the host galaxy environment.