Three-dimensional modeling of the HI kinematics of NGC 2915

International Centre for Radio Astronomy Research, The University of Western Australia, M468, 35 Stirling Highway, Crawley, WA 6009, Australia
Monthly Notices of the Royal Astronomical Society (Impact Factor: 5.11). 07/2011; 415(1):323 - 332. DOI: 10.1111/j.1365-2966.2011.18701.x
Source: arXiv


The nearby blue compact dwarf, NGC 2915, has its stellar disc embedded in a large, extended (∼22 B-band scalelengths) H i disc. New high-resolution H i synthesis observations of NGC 2915 have been obtained with the Australia Telescope Compact Array. These observations provide evidence of extremely complex H i kinematics within the immediate vicinity of the galaxy’s star-forming core. We identify and quantify double-peaked H i line profiles near the centre of the galaxy and show that the H i energetics can be accounted for by the mechanical energy output of the central high-mass stellar population within time-scales of 106–107 yr. Full three-dimensional models of the H i data cube are generated and compared to the observations to test various physical scenarios associated with the high-mass star-forming core of NGC 2915. Purely circular H i kinematics are ruled out together with the possibility of a high-velocity-dispersion interstellar medium at inner radii. Radial velocities of ∼30 km s−1 are required to describe the central-most H i kinematics of the system. Our results lend themselves to the simple physical scenario in which the young stellar core of the galaxy expels the gas outwards from the centre of the disc, thereby creating a central H i underdensity. These kinematics should be thought of as being linked to a central H i outflow rather than a large-scale galactic blowout or wind.

Download full-text


Available from: Renee C. Kraan-Korteweg, Oct 03, 2015
9 Reads
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: UGC 4483 is a nearby Blue Compact Dwarf (BCD) galaxy. HST observations have resolved the galaxy into single stars and this has led to the derivation of its star formation history and to a direct estimate of its stellar mass. We have analysed archival VLA observations of the 21-cm line and found that UGC 4483 has a steeply-rising rotation curve which flattens in the outer parts at a velocity of ~20 km/s. Radial motions of ~5 km/s may also be present. As far as we know, UGC 4483 is the lowest-mass galaxy with a differentially rotating HI disk. The steep rise of the rotation curve indicates that there is a strong central concentration of mass. We have built mass models using the HST information on the stellar mass to break the disk-halo degeneracy: old stars contribute ~50% of the observed rotation velocity at 2.2 disk scale-lengths. Baryons (gas and stars) constitute an important fraction of the total dynamical mass. These are striking differences with respect to typical dwarf irregular galaxies (dIrrs), which usually have slowly-rising rotation curves and are thought to be entirely dominated by dark matter. BCDs appear to be different from non-starbursting dIrrs in terms of their HI and stellar distributions and their internal dynamics. To their high central surface brightnesses and high central HI densities correspond strong central rotation-velocity gradients. This implies that the starburst is closely related with the gravitational potential and the concentration of gas. We discuss the implications of our results on the properties of the progenitors/descendants of BCDs.
    Astronomy and Astrophysics 07/2012; 544. DOI:10.1051/0004-6361/201219457 · 4.38 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Extended ultraviolet (XUV) discs have been found in a substantial fraction of late-type - S0, spiral and irregular - galaxies. Similarly, most late-type spirals have an extended gas disc, observable in the 21-cm radio line (H I). The morphology of galaxies can be quantified well using a series of scale-invariant parameters; concentration-asymmetry-smoothness (CAS), Gini, M20, and GM parameters. In this series of papers, we apply these to H I column density maps to identify mergers and interactions, lopsidedness and now XUV discs. In this paper, we compare the quantified morphology and effective radius (R50) of the Westerbork observations of neutral Hydrogen in Irregular and SPiral galaxies Project (WHISP) H I maps to those of far- and near-ultraviolet images obtained with GALEX, to explore how close the morphology and scales of H I and UV in these discs correlate. We find that XUV discs do not stand out by their effective radii in UV or H I. However, the concentration index in far-ultraviolet (FUV) appears to select some XUV discs. And known XUV discs can be identified via a criterion using asymmetry and M20; 80 per cent of XUV discs are included but with 55 per cent contamination. This translates into 61 candidate XUV disc out of our 266 galaxies, 23 per cent consistent with previous findings. Otherwise, the UV and H I morphology parameters do not appear closely related. Our motivation is to identify XUV discs and their origin. We consider three scenarios; tidal features from major mergers, the typical extended H I disc is a photo-dissociation product of the XUV regions and both H I and UV features originate in cold flows fueling the main galaxy. We define extended H I and UV discs based on their concentration (CHI > 5 and CFUV > 4 respectively), but that these two subsamples never overlap in the WHISP sample. This appears to discount a simple photo-dissociation origin of the outer H I disc. Previously, we identified the morphology space occupied by ongoing major mergers. Known XUV discs rarely reside in the merger-dominated part of H I morphology space but those that do are type 1. The exceptions, XUV discs in ongoing mergers, include the previously identified UGC 4862 and UGC 7081, 7651, and 7853. This suggests cold flows as the origin for the XUV complexes and their surrounding H I structures.
    Monthly Notices of the Royal Astronomical Society 12/2012; 427(4):3159-3175. DOI:10.1111/j.1365-2966.2012.21975.x · 5.11 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: For a rotating galaxy, the inner circular-velocity gradient d_{R}V(0) provides a direct estimate of the central dynamical mass density, including gas, stars, and dark matter. We consider 60 low-mass galaxies with high-quality HI and/or stellar rotation curves (including starbursting dwarfs, irregulars, and spheroidals), and estimate d_{R}V(0) as V(R_d)/R_d, where R_d is the galaxy scale-length. For gas-rich dwarfs, we find that V(R_d)/R_d correlates with the central surface brightness mu(0), the mean atomic gas surface density Sigma_gas, and the star formation rate surface density Sigma_SFR. Starbursting galaxies, such as blue compact dwarfs (BCDs), generally have higher values of V(R_d)/R_d than dwarf irregulars, suggesting that the starburst is closely related to the inner shape of the potential well. There are, however, some "compact" irregulars with values of V(R_d)/R_d similar to BCDs. Unless a redistribution of mass takes place, BCDs must evolve into compact irregulars. Rotating spheroidals in the Virgo cluster follow the same correlation between V(R_d)/R_d and mu(0) as gas-rich dwarfs. They have values of V(R_d)/R_d comparable to those of BCDs and compact irregulars, pointing at evolutionary links between these types of dwarfs. Finally, we find that, similarly to spiral galaxies and massive starbursts, the star-formation activity in dwarfs can be parametrized as Sigma_SFR = epsilon*Sigma_gas/t_orb, where t_orb is the orbital time and epsilon = 0.02.
    Astronomy and Astrophysics 11/2013; 563. DOI:10.1051/0004-6361/201322658 · 4.38 Impact Factor
Show more