Search

We report the detection of the ordered alignment between the magnetic field and kpc-scale bubbles in the nearby spiral galaxy, NGC 628. Applying the Velocity Gradient Technique on CO spectroscopic data from the ALMA-PHANGS, the magnetic field of NGC 628 is measured at the scale of 191 pc (∼4″). The large-scale magnetic field is oriented parallel to the spiral arms and curves around the galactic bubble structures in the mid-infrared emission observed by the James Webb Space Telescope. A total of 21 bubble structures have been identified at the edges of spiral arms with scales over 300 pc, which includes two kpc-scale structures. These bubbles are caused by supernova remnants and prolonged star formation and are similar to the outflow chimneys found in neutral hydrogen in galactic disks. At the edge of the bubbles, the shocks traced by the O iii emission present a curved magnetic field that parallels the bubble's shell. The magnetic field follows the bubble expansion and binds the gas in the shell to trigger further star formation. By analyzing the larger sample of 1694 bubbles, we found a distinct radial-size distribution of bubbles in NGC 628 indicating the star formation history in the galaxy. [ABSTRACT FROM AUTHOR]

Combining infrared and submillimeter observations and applying a two-temperature modified blackbody (TMBB) model with a hierarchical Bayesian technique, we model the spectral energy distribution of 12 nearby dwarf irregular (dIrr) galaxies. We aim to probe potential submillimeter excess emission at 350, 500, and 850 μm and investigate the properties of cold dust parameters. Based on the TMBB model with cold dust emissivity index (βc) fixed to 2, one galaxy shows 500 μm excess emission and nine galaxies show excess at 850 μm (five of them still show 850 μm excess in the case of free βc). We find that the 850 μm excess emission is easily detected in the dIrr galaxies with low star formation activity. The 850 μm excess is more frequent and more prominent in dIrr galaxies with low molecular hydrogen gas mass fraction or low ratios between cold dust mass and gas mass. As galaxies evolve, the ratios between atomic hydrogen gas mass and stellar mass decrease and the 850 μm excess emission tends to decrease or even disappear. Our results suggest that the cold dust temperature may increase, as the dIrr galaxies have more intense star formation or richer metallicity. There is a weak anticorrelation between the cold dust-to-stellar mass ratio and the specific star formation rate for our galaxies. [ABSTRACT FROM AUTHOR]

We mapped the kinetic temperature structure of Orion KL in a ∼20″ (∼8000 au) sized region with para-H2CS 707 − 606, 726 − 625, and 725 − 624 making use of Atacama Large Millimeter/submillimeter Array Band 6 Science Verification data. The kinetic temperatures obtained with a resolution of 1.″65 × 1.″14 (∼550 au) are deduced by modeling the measured averaged velocity-integrated intensity ratios of para-H2CS 726 − 625/707 − 606 and 725 − 624/707 − 606 with a RADEX non-LTE model. The kinetic temperatures of the dense gas, derived from the para-H2CS line ratios at a spatial density of 107 cm−3, are high, ranging from 43 to >500 K with an unweighted average of ∼170 K. There is no evidence for internal sources playing an important role in the heating of the various structures identified in previous work, namely the elongated ridge, the northwestern clump, and the eastern region of the compact ridge, while the high temperatures in the western region of the compact ridge may be dominated by internal massive star formation. Significant gradients of kinetic temperature along molecular filaments traced by H2CS indicate that the dense gas is heated by the shocks induced by the enigmatic explosive event which occurred several hundred years ago and greatly affected the energetics of the Orion KL region. Thus, with the notable exception of the western region of the compact ridge, the high temperatures of the dense gas in Orion KL are probably caused by shocks from the explosive event, leading to a dominant component of externally heated dense gas. [ABSTRACT FROM AUTHOR]

We select 13 nearby spiral galaxies from the Nearby Galaxies Legacy Survey (NGLS) project and perform spectral energy distribution fitting for each galaxy applying two-component modified blackbody models on a global scale aim to probe the potential submillimeter (submm) excess. We find that NGC 2976, NGC 3351, and NGC 4631 show excess emission at 850 μm when using βc = 2.0. The contributions of CO(3–2), free–free emission or synchrotron radiation cannot explain their 850 μm excess. Our results suggest that a submm excess at 850 μm may be more easily detected for galaxies with faint total infrared luminosity and low cold dust mass. The colder temperature of cold dust, the more radiation of dust there is at 850 μm. The submm excess are prone to be detected in spiral galaxies with low stellar mass. As the metallicity of galaxies become poor, the submm excess is more obvious. [ABSTRACT FROM AUTHOR]

The bubble G15.684-0.29 has a radius of 15.7 pc. Its large size indicates that it may have enough time to trigger star formation. We identify 39 dense cold clumps around the bubble from the Hi-GAL survey. All of them satisfy the criteria for forming massive stars, and most of them lie in the bubble shell. We identify 19 molecular clumps around the bubble from the 12CO(3–2) survey, all of which are gravitationally bound. We found 9 Class I YSOs, 28 Class II YSOs, and 12 transition disks (TDs) around the bubble. For those young stellar objects (YSOs) located within the bubble boundary, 6 of 7 Class I YSOs lie in the shell, 15 of 22 Class II YSOs lie inside the bubble, and 3 of 5 TDs lie inside the bubble. The dynamical age of G15.684-0.29 in a turbulent medium is ∼4 Myr, which is much greater than the shell fragmentation time, ∼0.82–1.74 Myr. We suggest that triggered star formation may be ongoing in the shell of the bubble, and the collect and collapse model may work here. However, we cannot rule out the possibility that the radiation-driven implosion model may work on the formation of some YSOs. As we expected, the larger bubble has a much longer dynamical age, but we failed to find a clear age gradient for YSOs around the bubble. [ABSTRACT FROM AUTHOR]