Pc Of NGC Research Articles

PHANGS–JWST First Results: The Dust Filament Network of NGC 628 and Its Relation to Star Formation Activity

PHANGS–JWST mid-infrared (MIR) imaging of nearby spiral galaxies has revealed ubiquitous filaments of dust emission in intricate detail. We present a pilot study to systematically map the dust filament network (DFN) at multiple scales between 25 and 400 pc in NGC 628. MIRI images at 7.7, 10, 11.3, and 21 μm of NGC 628 are used to generate maps of the filaments in emission, while PHANGS–HST B-band imaging yields maps of dust attenuation features. We quantify the correspondence between filaments traced by MIR thermal continuum/polycyclic aromatic hydrocarbon (PAH) emission and filaments detected via extinction/scattering of visible light; the fraction of MIR flux contained in the DFN; and the fraction of H ii regions, young star clusters, and associations within the DFN. We examine the dependence of these quantities on the physical scale at which the DFN is extracted. With our highest-resolution DFN maps (25 pc filament width), we find that filaments in emission and attenuation are cospatial in 40% of sight lines, often exhibiting detailed morphological agreement; that ∼30% of the MIR flux is associated with the DFN; and that 75%–80% of the star formation in H ii regions and 60% of the mass in star clusters younger than 5 Myr are contained within the DFN. However, the DFN at this scale is anticorrelated with looser associations of stars younger than 5 Myr identified using PHANGS–HST near-UV imaging. We discuss the impact of these findings on studies of star formation and the interstellar medium, and the broad range of new investigations enabled by multiscale maps of the DFN.

Understanding the secular evolution of NGC 628 using UltraViolet Imaging Telescope

ABSTRACT Secular and environmental effects play a significant role in regulating the star-formation rate and hence the evolution of the galaxies. Since ultraviolet (UV) flux is a direct tracer of the star formation in galaxies, the UltraViolet Imaging Telescope (UVIT) onboard AstroSat enables us to characterize the star-forming regions in a galaxy with its remarkable spatial resolution. In this study, we focus on the secular evolution of NGC 628, a spiral galaxy in the local Universe. We exploit the resolution of UVIT to resolve up to ∼63 pc in NGC 628 for identification and characterization of the star-forming regions. We identify 300 star-forming regions in the UVIT far-UV image of NGC 628 using ProFound and the identified regions are characterized using Starburst99 models. The age and mass distribution of the star-forming regions across the galaxy supports the inside-out growth of the disc. We find that there is no significant difference in the star-formation properties between the two arms of NGC 628. We also quantify the azimuthal offset of the star-forming regions of different ages. Since we do not find an age gradient, we suggest that the spiral density waves might not be the possible formation scenario of the spiral arms of NGC 628. The headlight cloud present in the disc of the galaxy is found to be having the highest star-formation rate density ($0.23 \, \mathrm{M}_{\odot } \, \mathrm{yr^{-1} \, kpc}^{-2}$) compared to other star-forming regions on spiral arms and the rest of the galaxy.

CO Excitation and its Connection to Star Formation at 200 pc in NGC 1365

We report high-resolution (2″ ∼ 200 pc) mappings of the central region of the nearby barred spiral galaxy NGC 1365 in the CO(1–0) and CO(2–1) emission lines. The 2–1/1–0 ratio of integrated intensities shows a large scatter (0.15) with a median value of 0.67. We also calculate the ratio of velocity dispersions and peak temperatures and find that in most cases the velocity dispersion ratio is close to unity and thus the peak temperature ratio is comparable to the integrated intensity ratio. This result indicates that both CO(1–0) and CO(2–1) lines trace similar components of molecular gas, with their integrated intensity (or peak temperature) ratios reflecting the gas density and/or temperature. Similar to recent kiloparsec-scale studies, these ratios show a positive correlation with a star formation rate indicator (here we use an extinction-corrected Hα map), suggesting that molecular gas associated with recent star formation is denser and/or warmer. We also find that some CO spectra show two peaks owing to complicated kinematics, and such two components likely trace molecular gas at different conditions. This result demonstrates the importance of spectral fitting to measure integrated intensities and their ratios more accurately.

The Distance and Origin of the Cometary Globule CG 12

Abstract The cometary globule CG 12 and its associated young cluster NGC 5367 is located at a Galactic latitude of b = 21°, and the origin of this high-latitude star formation event has been unclear. Getman et al. identified a nearby group of B stars and suggested they could be the remnant of a group of massive stars of which one exploded as a supernova. We here use Gaia EDR3 data to measure the accurate distance of NGC 5367 and the B-stars. We find a mean distance of 670 pc for NGC 5367 and 675 pc for the B-stars, strongly supporting the suggestion of Getman et al.

Envelope masses and distances to planetary nebulae: IC 5117 and NGC 7293

A technique for self-consistent determination of the mass of ionized gas M i in planetary nebulae (PNe) envelopes and the distance D to these nebulae is developed. The technique is based on the calculation of optimized photoionization models of their emission (OPMEs). Models of a “young” nebula (IC 5117) and an “old” one (NGC 7293) are calculated. The values M i = 0.0056M ⊙ and D = 1287 pc for IC 5117 and M i = 0.681M ⊙ and D = 201 pc for NGC 7293 are determined. The radial gas density distribution in a PN envelope was defined by an approximation expression that is close to the “normal” one and was found earlier based on the analysis of isophote maps of 12 PNe (Astron. Zh. 69, 1166–1178 (1992)). The mass of ionized gas in nebulae envelopes was determined in the process of OPME calculation by integrating the radial density distribution over the envelope volume. The distance to nebulae was also determined in the process of OPME calculation as one of its free parameters by comparing the model flux in the Hβ line at a distance to the Earth set by the optimizer with the corresponding observed flux. The values of D determined in such a manner are compared to the data from other studies.

INFRARED SPECTROSCOPY OF THE DIFFUSE IONIZED HALOS OF EDGE-ON GALAXIES

We present a study of ionized gas, PAHs, and molecular hydrogen emission in the halos of three edge-on galaxies, NGC 891, NGC 5775 and NGC 3044, based on 10-20 micron Spitzer Space Telescope spectra. The [Ne III]/[Ne II] ratio, an excellent measure of radiation hardness, rises with z in the halo of NGC 891. It is also higher in the halo of NGC 5775 than in the disk. NGC 3044 presents a more confusing situation. To explain the [Ne III]/[Ne II] as well as optical line ratio behavior in NGC 891, we carry out a simple exploration of parameter space with CLOUDY, which indicates a large increase in radiation temperature with height. Illustrative examples of physical models using a Monte Carlo radiative transfer code show that the rising neon ratio may be explained by adding a vertically extended, hot stellar source to a thin disk of massive stars. However, several other sources of hard spectra may be relevant. PAH features have scale heights of 430--530 pc in NGC 891 and 720--1080 pc in NGC 5775, suggesting they can be transported by disk-halo flows. Within NGC 891 and NGC 5775, scale heights are similar for all PAHs. For NGC 891, the scale heights exceed that of 8 micron emission, indicating a transition from more ionized to more neutral PAHs with height. Most PAH equivalent widths are higher in the halos. Molecular hydrogen 17.03 micron emission with scale heights of 550-580 pc in NGC 891 and 850 pc in NGC 5775 suggests a molecular component in a surprisingly thick layer.

BV photometry of a possible open star cluster pair NGC 7031/NGC 7086

AbstractWe present a CCD BV photometry of the possible binary open star cluster NGC 7031/NGC 7086. The aim is to confirm or disprove their common nature on the grounds of their age and distance. An age of 224 ± 25 Myr and a distance of 831 ± 72 pc was determined for NGC 7031, and 178 ± 25 Myr, 955 ± 84 pc for NGC 7086, respectively. Based on these differences in age and distance we conclude that the two clusters are most likely not formed together from one and the same giant molecular cloud and thus do not form a true binary cluster. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

HI and OH Absorption of the Nuclear Region of NGC 3079

We conducted an observation of weak HI and OH absorption features in the parsec-scale nuclear region of NGC 3079 using a global VLBI network; the VLBA, the VLA and the Green Bank 43-m telescope of NRAO. One mas corresponds to 0.076 pc in NGC 3079.

Synthesis Imaging of Dense Gas in Nearby Galaxies

We present images of the HCN J = 1-0 emission from five nearby spiral galaxies made with the Berkeley-Illinois-Maryland Association interferometer. The HCN observations comprise the first high-resolution (θ ~ 5''-10'') survey of dense molecular gas from a sample of normal galaxies, rather than galaxies with prolific starburst or nuclear activities. The images show compact structure, demonstrating that the dense gas emission is largely confined to the central kiloparsec of the sources. To within the uncertainties, 70%-100% of the single-dish flux is recovered for each source; this implies that there is not a significant contribution to the HCN flux from low-level emission in the disks of the galaxies. In one of the galaxies, NGC 6946, the ratio of HCN to CO integrated intensities ranges from 0.05-0.2 within the extent of the HCN emission (r = 150 pc), with an average value of 0.11 ± 0.01 over the whole region; the range and average values of the ratios in NGC 6946 are very similar to what is observed in the central r = 250 pc of the Milky Way. A comparison with single-dish observations allows us to place an upper limit of 0.01 on the ratio of integrated intensities in the region 150 < r < 800 pc in NGC 6946. In NGC 6946, NGC 1068 and the Milky Way, the ratio IHCN/ICO is 5-10 times higher in the bulge regions than in their disks; this suggests that the physical conditions in their bulges and disks are very different. Furthermore, the presence of dense gas on size scales of ~500 pc in the centers of these nearby galaxies and the Milky Way suggests that the internal pressure is at least 107 cm-3 K in their centers; this is some 3 orders of magnitude greater than the pressure in the local interstellar medium in the Milky Way, and it is 2 orders of magnitude greater than the pressure from the self-gravity of a solar neighborhood giant molecular cloud. In NGC 4826 and M51, as in the Milky Way and NGC 1068, there is a linear offset of ~100 pc between the dense gas distribution and the peak of the radio continuum emission. We did not detect HCN toward three additional spiral galaxies.

Motions in Barred Spiral Galaxies. I. The Nuclei of NGC 1097 and NGC 1365.

view Abstract Citations (84) References (7) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Motions in Barred Spiral Galaxies. I. The Nuclei of NGC 1097 and NGC 1365. Burbidge, E. Margaret ; Burbidge, G. R. Abstract The nuclear regions of the barred spirals NGC 1097 and NGC 1365 are shown and described. Spectra of these nuclei have been obtained, and the rotations have been measured from the Ha and [N ii] x 6583 emission lines. The rotation-curve of the nucleus of NGC 1097 is discontinuous in the inner part. The nuclear region in this galaxy consists of a small inner amorphous nucleus and an outer segmented annulus; the cause of the velocity discontinuity may be that the emission lines arise only in the annulus. The rotation-curve of NGC 1365 is linear across the nucleus. The observed rotations of both nuclei are quite large, the velocity difference from one side' to the other amounting to 413 km/sec in NGC 1097 and 431 km/sec in NGC 1365. If rotation alone is present, these, when corrected for orientation, give 549 km/sec across a diameter of about 20" or 1600 pc in NGC 1097 and 808 km/sec across a diameter of about 30" or 3000 pc in NGC 1365. It is stressed that the apparent rotational velocity might contain a component due to expansion in the planes' of the galaxies, whose magnitude could not be measured in objects whose major axes are not unequivocally determined from their geometry. Mass estimates of the nuclei from the rotations are 0.5-1.3 X 1011 `Mo in NGC 1097 and 2.2-3.4 X 1010 Mo in NGC 1365. These correspond to mean densities of >38 Mo/pc3 in NGC 1097 and 7-23 Mo/pc3 in NGC 1365. Publication: The Astrophysical Journal Pub Date: July 1960 DOI: 10.1086/146896 Bibcode: 1960ApJ...132...30B full text sources ADS | data products SIMBAD (2) NED (2) Related Materials (6) Part 2: 1960ApJ...132..654B Part 3: 1960ApJ...132..661B Part 4: 1962ApJ...136..119B Part 5: 1962ApJ...136..704B Part 6: 1964ApJ...140...85B Part 7: 1964ApJ...140...94R