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Register a new userA thorough view of the nuclear region of NGC 253 - Combined Herschel, SOFIA and APEX dataset
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Added by
Juan-Pablo Perez-Beaupuits
Publication date
2018
fields
Physics
and research's language is
English
Authors
J.P. Perez-Beaupuits
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We present a large set of spectral lines detected in the $40$ central region of the starburst galaxy NGC 253. Observations were obtained with the three instruments SPIRE, PACS and HIFI on board the Herschel Space Observatory, upGREAT on board of the SOFIA airborne observatory, and the ground based APEX telescope. Combining the spectral and photometry products of SPIRE and PACS we model the dust continuum Spectral Energy Distribution (SED) and the most complete $^{12}$CO Line SED reported so far toward the nuclear region of NGC 253. Properties and excitation of the molecular gas were derived from a three-component non-LTE radiative transfer model, using the SPIRE $^{13}$CO lines and ground based observations of the lower-$J$ $^{13}$CO and HCN lines, to constrain the model parameters. Three dust temperatures were identified from the continuum emission, and three components are needed to fit the full CO LSED. Only the third CO component (fitting mostly the HCN and PACS $^{12}$CO lines) is consistent with a shock/mechanical heating scenario. A hot core chemistry is also argued as a plausible scenario to explain the high-$J$ $^{12}$CO lines detected with PACS. The effect of enhanced cosmic ray ionization rates, however, cannot be ruled out, and is expected to play a significant role in the diffuse and dense gas chemistry. This is supported by the detection of ionic species like OH$^+$ and H$_2$O$^+$, as well as the enhanced fluxes of the OH lines with respect to those of H$_2$O lines detected in both PACS and SPIRE spectrum.
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We present observations of a massive star cluster near the nuclear region of the nearby starburst galaxy NGC 253. The peak of near-infrared emission, which is spatially separated by 4 from the kinematic center of the galaxy, is coincident with a super star cluster whose properties we examine with low-resolution (R ~ 1,200) infrared CTIO spectroscopy and optical/near-infrared HST imaging. Extinction, measured from [FeII] lines, is estimated at Av = 17.7 +/- 2.6. The age of the cluster is estimated at 5.7 Myr, based on Bry equivalent width for an instantaneous burst using Starburst99 modeling. However, a complex star formation history is inferred from the presence of both recombination emission and photospheric CO absorption. The ionizing photon flux has a lower limit of 7.3 +/- 2.5 x 10^53 inverse seconds, corrected for extinction. Assuming a Kroupa IMF, we estimate a cluster mass of 1.4 +/- 0.4 x 10^7 solar masses. We observe a strong Wolf-Rayet signature at 2.06 microns and report a weak feature at 2.19 microns which may be due to a massive stellar population, consistent with the derived mass and age of this cluster.
We present high-resolution spectral line and continuum VLBI and VLA observations of the nuclear region of NGC 253 at 22 GHz. While the water vapor masers in this region were detected on arcsecond and milliarcsecond scales, we could not detect any compact continuum emission with a 5 sigma upper limit of ~ 1 mJy. The observations reveal that the water maser emission is not related to a possible low-luminosity active galactic nucleus but is almost certainly associated with star-formation activity. Not detecting any compact continuum source on milliarcsecond scales also questions the presence of a - previously assumed - active nucleus in NGC 253.
NGC 253 is a starburst galaxy of SAB(s)c type with increasing interest because of its high activity at unrivaled closeness. Its energetic event is manifested as the vertical gas features in its central molecular zone, for which stellar feedback was proposed as the driving engine. In order to pursue details of the activity, we have undertaken a kinematic analysis of the ALMA archive data of CO($J$=3--2) emission at the highest resolution $sim$3 pc. We revealed that one of the non-rotating gas components in the central molecular zone shows a loop-like distribution of $sim$200 pc radius. The loop is associated with a star cluster, whereas the cluster is not inside the loop and is not likely as the driver of the loop formation. Further, we find that the bar potential of NGC 253 seems to be too weak to drive the gas motion by the eccentric orbit. As an alternative we frame a scenario that magnetic acceleration by the Parker instability is responsible for the creation of the loop. We show that the observed loop properties are similar to those in the Milky Way, and argue that recent magnetro-hydrodynamics simulations lend support for the picture having the magnetic field strength of $gtrsim$100 $mu$G. We suggest that cluster formation was triggered by the falling gas to the footpoint of the loop, which is consistent with a typical dynamical timescale of the loop $sim$1 Myr.
We present new maps of emission-line flux distributions and kinematics in both ionized (traced by HI and [FeII] lines) and molecular (H2) gas of the inner 0.7x0.7kpc2 of the galaxy NGC4303, with a spatial resolution 40-80pc and velocity resolution 90-150 km/s obtained from near-IR integral field specroscopy using the VLT instrument SINFONI. The most promiment feature is a 200-250pc ring of circum-nuclear star-forming regions. The emission from ionized and molecular gas shows distinct flux distributions: while the strongest HI and [FeII] emission comes from regions in the west side of the ring (ages~4Myr), the H2 emission is strongest at the nucleus and in the east side of the ring (ages>10Myr). We find that regions of enhanced hot H2 emission are anti-correlated with those of enhanced [FeII] and HI emission, which can be attributed to post starburst regions that do not have ionizing photons anymore but still are hot enough (~2000K) to excite the H2 molecule. The line ratios are consistent with the presence of an AGN at the nucleus. The youngest regions have stellar masses in the range 0.3-1.5E5 MSun and ionized and hot molecular gas masses of ~0.25-1.2E4 Msun and 2.5-5 Msun, respectively. The stellar and gas velocity fields show a rotation pattern, with the gas presenting larger velocity amplitudes than the stars, with a deviation observed for the H2 along the nuclear bar, where increased velocity dispersion is also observed, possibly associated with non circular motions along the bar. The stars in the ring show smaller velocity dispersion than the surroundings, that can be attributed to a cooler dynamics due to their recent formation from cool gas.
The massive star forming region W3 was observed with the faint object infrared camera for the SOFIA telescope (FORCAST) as part of the Short Science program. The 6.4, 6.6, 7.7, 19.7, 24.2, 31.5 and 37.1 um bandpasses were used to observe the emission of Polycyclic Aromatic Hydrocarbon (PAH) molecules, Very Small Grains and Big Grains. Optical depth and color temperature maps of W3A show that IRS2 has blown a bubble devoid of gas and dust of $sim$0.05 pc radius. It is embedded in a dusty shell of ionized gas that contributes 40% of the total 24 um emission of W3A. This dust component is mostly heated by far ultraviolet, rather than trapped Ly$alpha$ photons. This shell is itself surrounded by a thin ($sim$0.01 pc) photodissociation region where PAHs show intense emission. The infrared spectral energy distribution (SED) of three different zones located at 8, 20 and 25arcsec from IRS2, show that the peak of the SED shifts towards longer wavelengths, when moving away from the star. Adopting the stellar radiation field for these three positions, DUSTEM model fits to these SEDs yield a dust-to-gas mass ratio in the ionized gas similar to that in the diffuse ISM. However, the ratio of the IR-to-UV opacity of the dust in the ionized shell is increased by a factor $simeq$3 compared to the diffuse ISM.
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