We present and describe the astro-photometric catalog of more than 800,000 sources found in the Hubble Tarantula Treasury Project (HTTP). HTTP is a Hubble Space Telescope Treasury program designed to ...image the entire 30 Doradus region down to the sub-solar (~0.5 M sub(middot in circle)) mass regime using the Wide Field Camera 3 and the Advanced Camera for Surveys. We observed 30 Doradus in the near-ultraviolet (F275W, F336W), optical (F555W, F658N, F775W), and near-infrared (F110W, F160W) wavelengths. The stellar photometry was measured using point-spread function fitting across all bands simultaneously. The relative astrometric accuracy of the catalog is 0.4 mas. The astro-photometric catalog, results from artificial star experiments, and the mosaics for all the filters are available for download. Color-magnitude diagrams are presented showing the spatial distributions and ages of stars within 30 Dor as well as in the surrounding fields. HTTP provides the first rich and statistically significant sample of intermediate- and low-mass pre-main sequence candidates and allows us to trace how star formation has been developing through the region. The depth and high spatial resolution of our analysis highlight the dual role of stellar feedback in quenching and triggering star formation on the giant H II region scale. Our results are consistent with stellar sub-clustering in a partially filled gaseous nebula that is offset toward our side of the Large Magellanic Cloud.
The galaxies M82, NGC 253, NGC 1068, and NGC 4945 have been detected in gamma -rays by Fermi. Previously, we developed and tested a model for cosmic-ray interactions in the starburst galaxy M82. Now, ...we aim to explore the differences between starburst and active galactic nucleus (AGN) environments by applying our self-consistent model to the starburst galaxy NGC 253 and the Seyfert galaxy NGC 1068. Assuming a constant cosmic-ray acceleration efficiency by supernova remnants with Milky Way parameters, we calculate the cosmic-ray proton and primary and secondary electron/positron populations, predict the radio and gamma -ray spectra, and compare with published measurements. We find that our models easily fit the observed gamma -ray spectrum for NGC 253 while constraining the cosmic-ray source spectral index and acceleration efficiency. However, we encountered difficultly modeling the observed radio data and constraining the speed of the galactic wind and the magnetic field strength, unless the gas mass is less than currently preferred values. Additionally, our starburst model consistently underestimates the observed gamma -ray flux and overestimates the radio flux for NGC 1068; these issues would be resolved if the AGN is the primary source of gamma -rays. We discuss the implications of these results and make predictions for the neutrino fluxes for both galaxies.
Filamentary star formation in NGC 1275 Canning, R. E. A; Ryon, J. E; Gallagher, J. S ...
Monthly notices of the Royal Astronomical Society,
10/2014, Letnik:
444, Številka:
1
Journal Article
Recenzirano
Odprti dostop
We examine the star formation in the outer halo of NGC 1275, the central galaxy in the Perseus cluster (Abell 426), using far-ultraviolet and optical images obtained with the Hubble Space Telescope. ...We have identified a population of very young, compact star clusters with typical ages of a few Myr. The star clusters are organized on multiple kiloparsec scales. Many of these star clusters are associated with ‘streaks’ of young stars, the combination of which has a cometary appearance. We perform photometry on the star clusters and diffuse stellar streaks, and fit their spectral energy distributions to obtain ages and masses. These young stellar populations appear to be normal in terms of their masses, luminosities and cluster formation efficiency; <10 per cent of the young stellar mass is located in star clusters. Our data suggest star formation is associated with the evolution of some of the giant gas filaments in NGC 1275 that become gravitationally unstable on reaching and possibly stalling in the outer galaxy. The stellar streaks then could represent stars moving on ballistic orbits in the potential well of the galaxy cluster. We propose a model where star-forming filaments, switched on ∼50 Myr ago and are currently feeding the growth of the NGC 1275 stellar halo at a rate of ≈−2 to 3 M⊙ yr−1. This type of process may also build stellar haloes and form isolated star clusters in the outskirts of youthful galaxies.
Abstract
Extragalactic cosmic ray populations are important diagnostic tools for tracking the distribution of energy in nuclei and for distinguishing between activity powered by star formation versus ...active galactic nuclei (AGNs). Here, we compare different diagnostics of the cosmic ray populations of the nuclei of Arp 220 based on radio synchrotron observations and the recent γ-ray detection. We find the γ-ray and radio emission to be incompatible; a joint solution requires at minimum a factor of 4–8 times more energy coming from supernovae and a factor of 40–70 more mass in molecular gas than that is observed. We conclude that this excess of the γ-ray flux in comparison to all other diagnostics of star-forming activity indicates that there is an AGN present that is providing the extra cosmic rays, likely in the western nucleus.
We present a detailed clustering analysis of the young stellar population across the star-forming ring galaxy NGC 6503, based on the deep Hubble Space Telescope photometry obtained with the Legacy ...ExtraGalactic UV Survey. We apply a contour-based map analysis technique and identify in the stellar surface density map 244 distinct star-forming structures at various levels of significance. These stellar complexes are found to be organized in a hierarchical fashion with 95 per cent being members of three dominant super-structures located along the star-forming ring. The size distribution of the identified structures and the correlation between their radii and numbers of stellar members show power-law behaviours, as expected from scale-free processes. The self-similar distribution of young stars is further quantified from their autocorrelation function, with a fractal dimension of ∼1.7 for length-scales between ∼20 pc and 2.5 kpc. The young stellar radial distribution sets the extent of the star-forming ring at radial distances between 1 and 2.5 kpc. About 60 per cent of the young stars belong to the detected stellar structures, while the remaining stars are distributed among the complexes, still inside the ring of the galaxy. The analysis of the time-dependent clustering of young populations shows a significant change from a more clustered to a more distributed behaviour in a time-scale of ∼60 Myr. The observed hierarchy in stellar clustering is consistent with star formation being regulated by turbulence across the ring. The rotational velocity difference between the edges of the ring suggests shear as the driving mechanism for this process. Our findings reveal the interesting case of an inner ring forming stars in a hierarchical fashion.
High-resolution submillimeter line and continuum observations are important in probing the morphology, column density, and dynamics of the molecular gas and dust around obscured active galactic ...nuclei (AGNs). With high-resolution (0.̋06 × 0.̋05 (6 × 5 pc)) ALMA 690 GHz observations we have found bright (TB > 80 K) and compact (full width half maximum size (FWHM) size of 10 × 7 pc) CO 6−5 line emission in the nuclear region of the extremely radio-quiet galaxy NGC 1377. The CO 6−5 intensity is partially aligned with the previously discovered jet/outflow of NGC 1377 and is tracing dense (n > 104cm-3) hot molecular gas at the base of the outflow. The velocity structure is complex and shifts across the jet/outflow are discussed in terms of separate overlapping kinematical components or rotation. High-velocity gas (Δv ± 145km s-1) is detected inside r < 2−3 pc and we suggest that it is emerging from an inclined rotating disk or torus of position angle PA = 140° ± 20° with a dynamical mass of 3 × 106M⊙. This mass is consistent with that of a supermassive black hole (SMBH), as inferred from the M−σ relation. The gas mass of the proposed disk/torus constitutes <3% of the dynamical mass inside a radius of 3 pc. In contrast to the intense CO 6−5 line emission, we do not detect 690 GHz dust continuum in the nuclear region of NGC 1377. The upper limit of S(690 GHz) ≲ 2 mJy implies an H2 column density N(H2) < 3 × 1023cm-2 (averaged in the central 6 × 5 pc beam). This is inconsistent with a Compton thick (CT) source and we discuss the possibility that CT obscuration may instead be occurring on smaller subparsec scales or in a larger foreground structure. From SED fitting we suggest that half of the IR emission of NGC 1377 is nuclear and the rest, mostly the far-infrared (FIR), is emerging from larger scales. The extreme radio quietness, and the lack of emission from other star formation tracers, raise questions on the origin of the FIR emission. We discuss the possibility that it arises from AGN-heated dust along the minor axis.
The Radcliffe wave is a ∼3 kpc long coherent gas structure containing most of the star-forming complexes near the Sun. In this Letter we aim to find a Galactic context for the Radcliffe wave by ...looking into a possible relationship between the gas structure and the Orion (local) arm. We use catalogs of massive stars and young open clusters based on
Gaia
Early Data Release 3 (EDR3) astrometry, in conjunction with kiloparsec-scale 3D dust maps, to investigate the Galactic
XY
spatial distributions of gas and young stars. We find a quasi-parallel offset between the luminous blue stars and the Radcliffe wave, in that massive stars and clusters are found essentially inside and downstream from the Radcliffe wave. We examine this offset in the context of color gradients observed in the spiral arms of external galaxies, where the interplay between density wave theory, spiral shocks, and triggered star formation has been used to interpret this particular arrangement of gas and dust as well as OB stars, and outline other potential explanations as well. We hypothesize that the Radcliffe wave constitutes the gas reservoir of the Orion (local) arm, and that it presents itself as a prime laboratory to study the interface between Galactic structure, the formation of molecular clouds in the Milky Way, and star formation.
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