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Register a new userThe nearest extreme starburst: bubbles, young star clusters, and outflow in NGC 3256
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Added by
Sebastian Lipari L.
Publication date
2004
fields
Physics
and research's language is
English
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In this Work we report, for the extreme starburst in the IR merger NGC 3256: (i) The detection of 4 galactic bubbles, associated with SN explosions.(ii) The first analysis of the spatial distribution of young star clusters (YSC) candidates.(iii) The kinematic study of the ionized gas in the core of of the main optical nucleus, performed with HST STIS spectra. The shape of the rotation curve and the emission line profile could be explained by the presence in the core of YSC with outflow.
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We present Gemini optical spectroscopy of 23 young star clusters in NGC3256. We find that the cluster ages range are from few Myr to ~150 Myr. All these clusters are relatively massive (2--40)x 10^{5} msun$ and appear to be of roughly 1.5 zo metallicity. The majority of the clusters in our sample follow the same rotation curve as the gas and hence were presumably formed in the molecular-gas disk. However, a western subsample of five clusters has velocities that deviate significantly from the gas rotation curve. These clusters may either belong to the second spiral galaxy of the merger or may have formed in tidal-tail gas falling back into the system. We discuss our observations in light of other known cluster populations in merging galaxies, and suggest that NGC 3256 is similar to Arp 220, and hence may become an Ultra-luminous Infrared Galaxy as the merger progresses and the star-formation rate increases. Some of the clusters which appeared as isolated in our ground-based images are clearly resolved into multiple sub-components in the HST-ACS images. The same effect has been observed in the Antennae galaxies, showing that clusters are often not formed in isolation, but instead tend to form in larger groups or cluster complexes.
We present Gemini optical spectroscopy of three young star clusters in the western tidal tail of NGC3256. Compact star clusters (as opposed to dwarf-galaxy candidates) in tidal tails are rare, with these three clusters the first for which detailed quantitative spectroscopy has ever been obtained. We find that two of these clusters appear to be coeval, while the third is approximately two times older~200 Myr vs.~80 Myr). All three clusters are massive (1-3 x 10^5 msun) and appear to be of roughly solar metallicity. Additionally, the three clusters appear to be relatively large (R_eff = 10-20 pc), possibly reflecting weak compression at the time of formation and/or the weak influence of the tidal field of the galaxy. All three clusters have velocities consistent with the general trend of the HI velocities in the tidal tail. We conclude that if the loosely bound tail material of NGC 3256 gets stripped during future interactions of this galaxy within its group, these three clusters may become part of the intra-group medium.
We present XMM-Newton EPIC observations of the two nearby starburst merger galaxies NGC 3256 & NGC 3310. The broad-band (0.3-10 keV) integrated X-ray emission from both galaxies shows evidence of multi-phase thermal plasmas plus an underlying hard non-thermal power-law continuum. NGC 3256 is well-fit with a model comprising two MEKAL components (kT=0.6/0.9 keV) plus a hard power-law (Gamma=2), while NGC 3310 has cooler MEKAL components (kT=0.3/0.6 keV) and a harder power-law tail (Gamma=1.8). Chandra observations of these galaxies both reveal the presence of numerous discrete sources embedded in the diffuse emission, which dominate the emission above ~2 keV and are likely to be the source of the power-law emission. The thermal components show a trend of increasing absorption with higher temperature, suggesting that the hottest plasmas arise from supernova-heated gas within the disks of the galaxies, while the cooler components arise from outflowing galactic winds interacting with the ambient interstellar medium (ISM). We find no strong evidence for an active galactic nucleus (AGN) in either galaxy.
The nearby dwarf starburst galaxy NGC5253 hosts a number of young, massive star clusters, the two youngest of which are centrally concentrated and surrounded by thermal radio emission (the `radio nebula). To investigate the role of these clusters in the starburst energetics, we combine new and archival Hubble Space Telescope images of NGC5253 with wavelength coverage from 1500 Ang to 1.9 micron in 13 filters. These include H-alpha, P-beta, and P-alpha, and the imaging from the Hubble Treasury Program LEGUS (Legacy Extragalactic UV Survey). The extraordinarily well-sampled spectral energy distributions enable modeling with unprecedented accuracy the ages, masses, and extinctions of the 9 optically brightest clusters (M_V < -8.8) and the two young radio nebula clusters. The clusters have ages ~1-15 Myr and masses ~1x10^4 - 2.5x10^5 M_sun. The clusters spatial location and ages indicate that star formation has become more concentrated towards the radio nebula over the last ~15 Myr. The most massive cluster is in the radio nebula; with a mass 2.5x10^5 M_sun and an age ~1 Myr, it is 2-4 times less massive and younger than previously estimated. It is within a dust cloud with A_V~50 mag, and shows a clear nearIR excess, likely from hot dust. The second radio nebula cluster is also ~1 Myr old, confirming the extreme youth of the starburst region. These two clusters account for about half of the ionizing photon rate in the radio nebula, and will eventually supply about 2/3 of the mechanical energy in present-day shocks. Additional sources are required to supply the remaining ionizing radiation, and may include very massive stars.
NGC 4945 is a nearby (3.8 Mpc) galaxy hosting a nuclear starburst and Seyfert Type 2 AGN. We use the Atacama Large Millimeter/submillimeter Array (ALMA) to image the 93 GHz (3.2 mm) free-free continuum and hydrogen recombination line emission (H40$alpha$ and H42$alpha$) at 2.2 pc (0.12) resolution. Our observations reveal 27 bright, compact sources with FWHM sizes of 1.4 - 4.0 pc, which we identify as candidate super star clusters. Recombination line emission, tracing the ionizing photon rate of the candidate clusters, is detected in 15 sources, 6 of which have a significant synchrotron component to the 93 GHz continuum. Adopting an age of ~5 Myr, the stellar masses implied by the ionizing photon luminosities are $log_{10}$($M_{star}$/M$_{odot}$) $approx$ 4.7 - 6.1. We fit a slope to the cluster mass distribution and find $beta = -1.8 pm 0.4$. The gas masses associated with these clusters, derived from the dust continuum at 350 GHz, are typically an order of magnitude lower than the stellar mass. These candidate clusters appear to have already converted a large fraction of their dense natal material into stars and, given their small free-fall times of ~0.05 Myr, are surviving an early volatile phase. We identify a point-like source in 93 GHz continuum emission which is presumed to be the AGN. We do not detect recombination line emission from the AGN and place an upper limit on the ionizing photons which leak into the starburst region of $Q_0 < 10^{52}$ s$^{-1}$.
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