The Localized Chemical Pollution in NGC 5253 Revisited: Results from Deep Echelle Spectrophotometry

López-Sánchez, Á. R.; Esteban, C.; García‐Rojas, J.; Peimbert, M.; Rodríguez, Mónica

doi:10.1086/510112

Cited by 143 publications

(224 citation statements)

References 71 publications

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“…To obtain gas mass, we need a gas-to-dust ratio (GTD). Scaled as the oxygen abundance of NGC 5253, 0.2-0.3 solar 13,14 , GTD~650, within the range 340-1200 inferred for the Magellanic clouds 15,16,17 . The observed dust mass is five times larger than the ~3000 M ¤ of dust expected for a 2 x 10 6 M ¤ gas cloud at GTD = 650.…”

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confidence: 71%

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Highly efficient star formation in NGC 5253 possibly from stream-fed accretion

Turner

Beck

Benford

et al. 2015

Nature

103

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Gas clouds in present-day galaxies are inefficient at forming stars. Low star formation efficiency is a critical parameter in galaxy evolution: it is why stars are still forming nearly fourteen billion years after the Big Bang 1 and why star clusters generally do not survive their births, instead dispersing to form galactic disks, halos, or bulges 2 . Yet the existence of ancient massive star clusters in the Milky Way, globular clusters, suggests that efficiencies were higher when they formed ten billion years ago. A local dwarf galaxy, NGC 5253, has a young star cluster that may provide an example of highly efficient star formation 3 . Here we report the detection of the J= 3-2 rotational transition of CO at the location of the massive cluster. The gas cloud is hot, dense, quiescent, and extremely dusty. Its gas-to-dust ratio is lower than the Galactic value, which we attribute to dust enrichment by the embedded star cluster. Its star formation efficiency exceeds 50%, ten times higher than clouds in the Milky Way: this cloud is a factory of stars and soot. We suggest that high efficiency results from the force-feeding of star formation by a streamer of gas falling into the galaxy.The Submillimeter Array image of NGC 5253, shown in Figure 1, reveals a bright CO(3-2) source coincident with the giant cluster and its "supernebula" 4 . "Cloud D" 3 is one of only two molecular clouds detected within the galaxy; the second cloud is smaller and located ~5" (90 pc) to the southwest. A "streamer" of gas extending along the minor axis is also detected in CO(3-2). This streamer, previously detected in lower J CO lines, appears to be falling into the galaxy near the supernebula 3,5 . Both the streamer and Cloud D emit 870µm continuum emission, as shown in Figure 2. Also shown is an image of 350µm continuum, in which both Cloud D and the streamer are detected. Figure 1. CO J=3-2 emission in NGC 5253. The SMA CO(3-2) integrated line intensity, in red, is shown atop a λ814nm Hubble Space Telescope image. The SMA beam is 4" x 2" (74 pc x 37 pc). The field covers 40" x 40" (740 pc x740 pc), north up, east left. Image registration is to < 1". The CO streamer coincides with the optical dust lane to the east. The massive star cluster is located at the bright CO peak, Cloud D; it is embedded 8.9 , and not visible here. Cloud F is to the southwest of Cloud D.The molecular gas in Cloud D is hot. This is clear from the increase in brightness from CO(2-1) 3 to CO(3-2). The intensity ratio of the two lines is I 32 /I 21 = 2.6±0.5 (I line = ∫T line dv). This ratio is nonthermal, although the thermal limit of 2.25 (~ν 2 ) is within the uncertainties, and is what we adopt. Non-LTE modeling of this ratio using RADEX 6 indicates a minimum kinetic temperature of T K > 200 K for the 1σ lower limit, and T K > 350 K for the adopted value of I 32 /I 21 = 2.25 (see Methods). The high gas temperature is consistent with a thermal origin for H 2 2.2µm emission in the region 7 . Cloud D appears to be a Photon-Dominated Region (PDR), heated by ultraviol...

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confidence: 71%

“…53 3) The cluster must be old enough to have Wolf-Rayet (WR) stars, which would explain the WR spectral signatures 13,14,50,51,54,55 . 4) The cluster must have mass less than the virial mass of 1.8 x 10 6 M ¤ , which is also the maximum mass allowed by the [SIV] and Brackett α linewidths 56,57 .…”

Section: Methodsmentioning

confidence: 99%

Highly efficient star formation in NGC 5253 possibly from stream-fed accretion

Turner

Beck

Benford

et al. 2015

Nature

103

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“…We calculated the N/O and Ne/O abundance ratios assuming that N/O = N + /O + and Ne/O = Ne ++ /O ++ , based on the similarity of the ionization potentials of the ions involved (Peimbert & Costero 1969). This ICF scheme has been used in previous work (e.g., López-Sánchez et al 2007;Hägele et al 2008;Bresolin et al 2009) and is a good approximation for high ionization degree objects. In our spectra, neon is seen via the [NeIII] emission line at 3869 Å.…”

Section: )mentioning

confidence: 99%

Gemini GMOS spectroscopy of HeII nebulae in M 33

Kehrig

Oey

Crowther

et al. 2011

A&A

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We have carried out a narrow-band survey of the Local Group galaxy, M 33, in the HeII λ4686 emission line, to identify HeII nebulae in this galaxy. With spectroscopic follow-up observations, we confirm three of seven candidate objects, including identification of two new HeII nebulae, BCLMP651, HBW673. We also obtain spectra of associated ionizing stars for all the HII regions, identifying two new WN stars. We demonstrate that the ionizing source for the known HeII nebula, MA 1, is consistent with being the earlytype WN star MC8 (M 33-WR14), by carrying out a combined stellar and nebular analysis of MC8 and MA 1. We were unable to identify the helium ionizing sources for HBW 673 and BCLMP 651, which do not appear to be Wolf-Rayet stars. According to the [OIII]λ5007/Hβ vs.[NII]λ6584/Hα diagnostic diagram, excitation mechanisms apart from hot stellar continuum are needed to account for the nebular emission in HBW 673, which appears to have no stellar source at all.

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“…Another remarkable feature of the starburst region in NGC 5253 is the presence of nitrogen-enriched (by a factor of 2-3) nebular material (Walsh & Roy 1987;Kobulnicky et al 1997;López-Sánchez et al 2007). MonrealIbero et al (2010) have mapped the area of nitrogen enrichment and find it peaks in the giant H ii region, which contains the two nuclear star clusters, and extends up to distances of 3 .3 (50 pc).…”

Section: Introductionmentioning

confidence: 99%

The very massive star content of the nuclear star clusters in NGC 5253

2016

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The blue compact dwarf galaxy NGC 5253 hosts a very young starburst containing twin nuclear star clusters, separated by a projected distance of 5 pc. One cluster (#5) coincides with the peak of the Hα emission and the other (#11) with a massive ultracompact H ii region. A recent analysis of these clusters shows that they have a photometric age of 1 ± 1 Myr, in apparent contradiction with the age of 3-5 Myr inferred from the presence of Wolf-Rayet features in the cluster #5 spectrum. We examine Hubble Space Telescope ultraviolet and Very Large Telescope optical spectroscopy of #5 and show that the stellar features arise from very massive stars (VMS), with masses greater than 100 M , at an age of 1-2 Myr. We further show that the very high ionizing flux from the nuclear clusters can only be explained if VMS are present. We investigate the origin of the observed nitrogen enrichment in the circum-cluster ionized gas and find that the excess N can be produced by massive rotating stars within the first 1 Myr. We find similarities between the NGC 5253 cluster spectrum and those of metal poor, high redshift galaxies. We discuss the presence of VMS in young, star-forming galaxies at high redshift; these should be detected in rest frame UV spectra to be obtained with the James Webb Space Telescope. We emphasize that population synthesis models with upper mass cut-offs greater than 100 M are crucial for future studies of young massive star clusters at all redshifts.

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The Localized Chemical Pollution in NGC 5253 Revisited: Results from Deep Echelle Spectrophotometry

Cited by 143 publications

References 71 publications

Highly efficient star formation in NGC 5253 possibly from stream-fed accretion

Highly efficient star formation in NGC 5253 possibly from stream-fed accretion

Gemini GMOS spectroscopy of HeII nebulae in M 33

The very massive star content of the nuclear star clusters in NGC 5253

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