High-Resolution Radio Maps of Wolf-Rayet Galaxies: Optically Thick H [CSC]ii[/CSC] Regions?

Beck, S. C.; Turner, Jean L.; Kovo, O.

doi:10.1086/301448

Cited by 57 publications

(100 citation statements)

References 30 publications

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“…If the beam is not centered on the galaxy (in the case of unresolved galaxies) or is not centered on a bright knot of emission (in the case of resolved galaxies), the smaller beams could contain even less flux than would be expected after corrections for the beams' areas. NGC 1741 and NGC 4490 are likely affected by pointing offsets, as seen by comparing the GBT pointing in Table 1 to previous radio continuum maps in Figure 2 of Beck et al (2000) and Figure 4 of Aversa et al (2011). As described in Section 2.2, pointing offsets from the peak of radio continuum emission result in the need for larger beam correction factors than derived from the archival radio continuum data, the lack of which result in steep spectra at the observed frequencies.…”

Section: Galaxies With Steep Radio Spectramentioning

confidence: 88%

“…T72 denotes galaxies that were observed, but not detected, by Tovmassian (1972) at 9.5 mm (31.6 GHz). T94 (Turner & Ho 1994), B00 (Beck et al 2000), B02 (Beck et al 2002), B03 (Beswick et al 2003), C04 (Chyży & Beck 2004), J04 (Johnson et al 2004), L04 (Lisenfeld et al 2004), R05 (Rosa-González 2005), T06 (Tsai et al 2006), B07 (Beck et al 2007), R08 (Reines et al 2008), J09 (Johnson et al 2009), D11 (Dumas et al 2011), K11 (Kodilkar et al 2011), and A11 (Aversa et al 2011) denote galaxies that were observed at lower frequencies. The galaxies are described in more detail in these papers.…”

Section: Introductionmentioning

confidence: 99%

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Radio Continuum Observations of Local Star-Forming Galaxies Using the Caltech Continuum Backend on the Green Bank Telescope

Rabidoux

Pisano

Kepley

et al. 2013

ApJ

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We observed radio continuum emission in 27 local (D < 70 Mpc) star-forming galaxies with the Robert C. Byrd Green Bank Telescope between 26 GHz and 40 GHz using the Caltech Continuum Backend. We obtained detections for 22 of these galaxies at all four sub-bands and four more marginal detections by taking the average flux across the entire bandwidth. This is the first detection (full or marginal) at these frequencies for 22 of these galaxies. We fit spectral energy distributions (SEDs) for all of the four sub-band detections. For 14 of the galaxies, SEDs were best fit by a combination of thermal free-free and nonthermal synchrotron components. Eight galaxies with four sub-band detections had steep spectra that were only fit by a single nonthermal component. Using these fits, we calculated supernova rates, total number of equivalent O stars, and star formation rates within each ∼23 beam. For unresolved galaxies, these physical properties characterize the galaxies' recent star formation on a global scale. We confirm that the radio-far-infrared correlation holds for the unresolved galaxies' total 33 GHz flux regardless of their thermal fractions, though the scatter on this correlation is larger than that at 1.4 GHz. In addition, we found that for the unresolved galaxies, there is an inverse relationship between the ratio of 33 GHz flux to total far-infrared flux and the steepness of the galaxy's spectral index between 1.4 GHz and 33 GHz. This relationship could be an indicator of the timescale of the observed episode of star formation.

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Section: Galaxies With Steep Radio Spectramentioning

confidence: 88%

Section: Introductionmentioning

confidence: 99%

Radio Continuum Observations of Local Star-Forming Galaxies Using the Caltech Continuum Backend on the Green Bank Telescope

Rabidoux

Pisano

Kepley

et al. 2013

ApJ

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“…Then the radio spectrum can be fit by models of homogeneous, isothermal, dust-free, ionization bounded regions of ionized gas, to obtain the turnover frequency ν t , the EM, n e , and infer the size D of the region (e.g., Deeg et al 1993;Johnson et al 2001;Hunt et al 2004). Alternatively, the optically thick and optically thin regions of the radio spectrum can be separated to constrain ν t , and thus infer the emission measure EM, size D, and rms electron density n e (e.g., Gordon 1988;Beck et al 2000).…”

Section: Extragalactic Radio Data Setsmentioning

confidence: 99%

The size-density relation of extragalactic H II regions

Hunt¹,

Hirashita²

2009

A&A

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Aims. We investigate the size-density relation in extragalactic H ii regions, with the aim of understanding the role of dust and different physical conditions in the ionized medium.Methods. First, we compiled several observational data sets for Galactic and extragalactic H ii regions and confirm that extragalactic H ii regions follow the same size (D)-density (n) relation as Galactic ones (n ∝ D −1 ), rather than a relation with constant luminosity (n ∝ D −1.5 ). Motivated by the inability of static models to explain this, we then modelled the evolution of the size-density relation of H ii regions by considering their star formation history, the effects of dust, and pressure-driven expansion. The results are compared with our sample data whose size and density span roughly six orders of magnitude. Results. The extragalactic samples cannot be understood as an evolutionary sequence with a single initial condition. Thus, the sizedensity relation does not result from an evolutionary sequence of H ii regions but rather reflects a sequence with different initial gas densities ("density hierarchy"). We also find that the size of many H ii regions is limited by dust absorption of ionizing photons, rather than consumption by ionizing neutral hydrogen. Dust extinction of ionizing photons is particularly severe over the entire lifetime of compact H ii regions with typical gas densities of > ∼ 10 3 cm −3 . Hence, as long as the number of ionizing photons is used to trace massive star formation, much star-formation activity could be missed. Such compact dense environments, the ones most profoundly obscured by dust, have properties similar to "maximum-intensity starbursts". This implies that submillimeter and infrared wavelengths may be necessary to accurately assess star formation in these extreme conditions both locally and at high redshift.

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“…Narrowband imaging may also be important to track the faintest youngest members of the population, which may not be detected with broadband IR imaging, although they are bright in narrow filters tuned to the recombination lines of their HIIRs (AlonsoHerrero et al 2002). Radio and mid-IR observations have uncovered still more heavily embedded regions of massive star formation that are heavily obscured even at 2 m (e.g., Kobulnicky & Johnson 1999;Beck et al 2000Beck et al , 2001Vacca et al 2002;Cabanac et al 2005); these objects are very young, dense, compact HIIRs that are the massive analogs of ultracompact H ii regions (UCHIIs). Hence they are dubbed ultradense HIIRs, or UDHIIs, by Kobulnicky & Johnson (1999), and they are the supposed precursors of optically visible SSCs.…”

Section: Introductionmentioning

confidence: 99%

Feedback in the Antennae Galaxies (NGC 4038/9). I. High‐Resolution Infrared Spectroscopy of Winds from Super Star Clusters

Gilbert

Graham

2007

ApJ

103

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We present high-resolution (R $ 24;600) near-IR spectroscopy of the youngest super star clusters (SSCs) in the prototypical starburst merger, the Antennae galaxies. These SSCs are young (3Y7 Myr old) and massive (10 5 Y10 7 M for a Kroupa initial mass function), and their spectra are characterized by broad, extended Brackett (Br ) emission, so we refer to them as emission-line clusters (ELCs) to distinguish them from older SSCs. The Br lines of most ELCs have supersonic widths (60Y110 km s À1 FWHM) and non-Gaussian wings whose velocities exceed the clusters' escape velocities. This high-velocity unbound gas is flowing out in winds that are powered by the clusters' massive O and Wolf-Rayet stars over the course of at least several crossing times. The large sizes of some ELCs relative to those of older SSCs may be due to expansion caused by these outflows; many of the ELCs may not survive as bound stellar systems, but rather dissipate rapidly into the field population. The observed tendency of older ELCs to be more compact than young ones is consistent with the preferential survival of the most concentrated clusters at a given age.

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High-Resolution Radio Maps of Wolf-Rayet Galaxies: Optically Thick H [CSC]ii[/CSC] Regions?

Cited by 57 publications

References 30 publications

Radio Continuum Observations of Local Star-Forming Galaxies Using the Caltech Continuum Backend on the Green Bank Telescope

Radio Continuum Observations of Local Star-Forming Galaxies Using the Caltech Continuum Backend on the Green Bank Telescope

The size-density relation of extragalactic H II regions

Feedback in the Antennae Galaxies (NGC 4038/9). I. High‐Resolution Infrared Spectroscopy of Winds from Super Star Clusters

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