Search for: All records

In this work, we constrain the star-forming properties of all possible sites of incipient high-mass star formation in the Milky Way’s Galactic Center. We identify dense structures using the CMZoom 1.3 mm dust continuum catalog of objects with typical radii of ∼0.1 pc, and measure their association with tracers of high-mass star formation. We incorporate compact emission at 8, 21, 24, 25, and 70μm from the Midcourse Space Experiment, Spitzer, Herschel, and SOFIA, cataloged young stellar objects, and water and methanol masers to characterize each source. We find an incipient star formation rate (SFR) for the Central Molecular Zone (CMZ) of ∼0.08M_⊙yr⁻¹over the next few 10⁵yr. We calculate upper and lower limits on the CMZ’s incipient SFR of ∼0.45 and ∼0.05M_⊙yr⁻¹,respectively, spanning roughly equal to and several times greater than other estimates of CMZ’s recent SFR. Despite substantial uncertainties, our results suggest the incipient SFR in the CMZ may be higher than previously estimated. We find that the prevalence of star formation tracers does not correlate with source volume density, but instead ≳75% of high-mass star formation is found in regions above a column density ratio (N_SMA/N_Herschel) of ∼1.5. Finally, we highlight the detection ofatoll sources, a reoccurring morphology of cold dust encircling evolved infrared sources, possibly representing Hiiregions in the process of destroying their envelopes.

 

Abstract We present high-resolution (∼2–3″; ∼0.1 pc) radio observations of the Galactic center cloud M0.10−0.08 using the Very Large Array at K and Ka band (∼25 and 36 GHz). The M0.10−0.08 cloud is located in a complex environment near the Galactic center Radio Arc and the adjacent M0.11−0.11 molecular cloud. From our data, M0.10−0.08 appears to be a compact molecular cloud (∼3 pc) that contains multiple compact molecular cores (5+; <0.4 pc). In this study, we detect a total of 15 molecular transitions in M0.10−0.08 from the following molecules: NH 3 , HC 3 N, CH 3 OH, HC 5 N, CH 3 CN, and OCS. We have identified more than sixty 36 GHz CH 3 OH masers in M0.10−0.08 with brightness temperatures above 400 K and 31 maser candidates with temperatures between 100 and 400 K. We conduct a kinematic analysis of the gas using NH 3 and detect multiple velocity components toward this region of the Galactic center. The bulk of the gas in this region has a velocity of 51.5 km s −1 (M0.10−0.08) with a lower-velocity wing at 37.6 km s −1 . We also detect a relatively faint velocity component at 10.6 km s −1 that we attribute to being an extension of the M0.11−0.11 cloud. Analysis of the gas kinematics, combined with past X-ray fluorescence observations, suggests M0.10−0.08 and M0.11−0.11 are located in the same vicinity of the Galactic center and could be physically interacting. 

The neutral hydrogen 21-cm line is an excellent tracer of the atomic interstellar medium in the cold and the warm phases. Combined 21-cm emission and absorption observations are very useful to study the properties of the gas over a wide range of density and temperature. In this work, we have used 21-cm absorption spectra from recent interferometric surveys, along with the corresponding emission spectra from earlier single dish surveys to study the properties of the atomic gas in the Milky Way. In particular, we focus on a comparison of properties between lines of sight through the gas disc in the Galactic plane and high Galactic latitude lines of sight through more diffuse gas. As expected, the analysis shows a lower average temperature for the gas in the Galactic plane compared to that along the high latitude lines of sight. The gas in the plane also has a higher molecular fraction, showing a sharp transition and flattening in the dust–gas correlation. On the other hand, the observed correlation between 21-cm brightness temperature and optical depth indicates some intrinsic difference in spin temperature distribution and a fraction of gas in the Galactic plane having intermediate optical depth (for 0.02 < τ < 0.2) but higher spin temperature, compared to that of the diffuse gas at high latitude with the same optical depth. This may be due to a small fraction of cold gas with slightly higher temperature and lower density present on the Galactic plane.

 

We present a comparison of low-J¹³CO and CS observations of four different regions in the LMC—the quiescent Molecular Ridge, 30 Doradus, N159, and N113, all at a resolution of ∼3 pc. The regions 30 Dor, N159, and N113 are actively forming massive stars, while the Molecular Ridge is forming almost no massive stars, despite its large reservoir of molecular gas and proximity to N159 and 30 Dor. We segment the emission from each region into hierarchical structures using dendrograms and analyze the sizes, masses, and line widths of these structures. We find that the Ridge has significantly lower kinetic energy at a given size scale and also lower surface densities than the other regions, resulting in higher virial parameters. This suggests that the Ridge is not forming massive stars as actively as the other regions because it has less dense gas and not because collapse is suppressed by excess kinetic energy. We also find that these physical conditions and energy balance vary significantly within the Ridge and that this variation appears only weakly correlated with distance from sites of massive-star formation such as R136 in 30 Dor, which is ∼1 kpc away. These variations also show only a weak correlation with local star formation activity within the clouds.

 

Abstract We present the ALMA detection of molecular outflowing gas in the central regions of NGC 4945, one of the nearest starbursts and also one of the nearest hosts of an active galactic nucleus (AGN). We detect four outflow plumes in CO J = 3 − 2 at ∼0.″3 resolution that appear to correspond to molecular gas located near the edges of the known ionized outflow cone and its (unobserved) counterpart behind the disk. The fastest and brightest of these plumes has emission reaching observed line-of-sight projected velocities of over 450 km s −1 beyond systemic, equivalent to an estimated physical outflow velocity v ≳ 600 km s −1 for the fastest emission. Most of these plumes have corresponding emission in HCN or HCO + J = 4 − 3. We discuss a kinematic model for the outflow emission where the molecular gas has the geometry of the ionized gas cone and shares the rotation velocity of the galaxy when ejected. We use this model to explain the velocities we observe, constrain the physical speed of the ejected material, and account for the fraction of outflowing gas that is not detected due to confusion with the galaxy disk. We estimate a total molecular mass outflow rate M ̇ mol ∼ 20 M ⊙ yr −1 flowing through a surface within 100 pc of the disk midplane, likely driven by a combination of the central starburst and AGN.