The Radio Continuum of the Metal‐deficient Blue Compact Dwarf Galaxy SBS 0335−052

Hunt, L. K.; Dyer, K. K.; Thuan, T. X.; Ulvestad, J. S.

doi:10.1086/383084

Cited by 47 publications

(97 citation statements)

References 56 publications

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“…At 1.3 cm and 2 cm, our high-resolution observations recover all the flux in SBS 0335−052 reported by Hunt et al (2004). This implies that the size of the entire thermal source at high frequencies must be smaller than or comparable to the 0.…”

Section: Location and Morphology Of The Radio Emissionsupporting

confidence: 80%

“…7 Because the lowfrequency radio flux is dominated by synchrotron emission, this nonthermal emission is likely to be associated with SNe from a distinct episode of star formation with an age of 3.5 Myr. At 6 cm, the lowest frequency of the observations presented here, we recover only 44% of the global flux measured by Hunt et al (2004). This would imply that the nonthermal emission is much more diffuse than the thermal; indeed if the significant synchrotron halo of I Zw 18 (Hunt et al 2005b), another lowmetallicity BCD, were placed at the distance of SBS 0335−052, it would be resolved out by our observations (see Section 5.4).…”

Section: Location and Morphology Of The Radio Emissionmentioning

confidence: 54%

“…To gain insight into the physical conditions in the radio sources present in SBS 0335−052, we apply a general thermal+nonthermal fit with an absorption component as in Hunt et al (2004). These are simple models that assume a uniform-density homogeneous ionized medium.…”

Section: Modeling the Spectral Energy Distributionsmentioning

confidence: 99%

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Probing Star Formation at Low Metallicity: The Radio Emission of Super Star Clusters in SBS 0335–052

Johnson

Hunt²,

Reines

2009

The Astronomical Journal

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We present high-resolution radio-continuum observations of the nascent starburst in the metal-poor galaxy SBS 0335−052. These radio data were taken with the Very Large Array and include observations at 0.7 cm, 1.3 cm, 2 cm, 3.6 cm, and 6 cm. These observations enable us to probe the thermal radio nebulae associated with the extremely young star-forming regions in this galaxy. Two discrete and luminous star-forming regions are detected in the south of the galaxy that appear to be associated with massive star clusters previously identified at optical wavelengths. However, the remaining optically identified massive star clusters are not clearly associated with radio emission (either thermal or nonthermal) down to the sensitivity limits of these radio data. The spectral energy distributions (SEDs) of the two radio-detected clusters are consistent with being purely thermal, and the entire region has an inferred ionizing flux of ∼1.2 × 10 53 s −1 , which is equivalent to ∼12,000 "typical" O-type stars (type O7.5 V). The observations presented here have resolved out a significant contribution from diffuse nonthermal emission detected previously, implying a previous episode of significant star formation. The current star formation rate (SFR) for this southern region alone is ∼1.3 M yr −1 , or ∼23 M yr −1 kpc −2 , which is nearing the maximum starburst intensity limit. This SFR derived from thermal radio emission also suggests that previous optical recombination line studies do not detect a significant fraction of the current star formation in SBS 0335−052. From model fits to the radio SED, we infer a global mean density in the two youngest clusters of n e 10 3 -10 4 cm −3 . In addition, a comparison between the compact and diffuse radio emission indicates that up to ∼50% of the ionizing flux could be leaking out of the compact H ii regions; this in is agreement with previous work, which suggests that the interstellar medium surrounding the natal clusters in SBS 0335−052 is porous and clumpy.

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Section: Location and Morphology Of The Radio Emissionsupporting

confidence: 80%

Section: Location and Morphology Of The Radio Emissionmentioning

confidence: 54%

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Probing Star Formation at Low Metallicity: The Radio Emission of Super Star Clusters in SBS 0335–052

Johnson

Hunt²,

Reines

2009

The Astronomical Journal

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“…In other cases (NGC 4214, NGC 1741, Mrk 8, Mrk 33, VII Zw 19, Pox 4, Tol 35, Mrk 1236NGC 6946, NGC 253, M 33: Johnson et al 2001;SBS 0335-052: Hunt et al 2004;Johnson et al 2009), the spatial resolution is insufficient to resolve the regions. 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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“…As in Bot et al (2010b), the thermal dust emission is adjusted according to the Draine & Li (2007) dust model. The free-free emission is deduced from the H α integrated flux, using the expression from Hunt et al (2004), assuming an electronic temperature T e = 10 4 K, the ratio of ionised helium to hydrogen n He + /n + H = 0.087, and no extinction. The synchrotron emission was fitted to the radio data from the literature as in Israel et al (2010).…”

Section: Integrated Sedsmentioning

confidence: 99%

Planckearly results. XVII. Origin of the submillimetre excess dust emission in the Magellanic Clouds

Ade¹,

Aghanim²,

Arnaud³

et al. 2011

A&A

123

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The integrated spectral energy distributions (SED) of the Large Magellanic Cloud (LMC) and Small Magellanic Cloud (SMC) appear significantly flatter than expected from dust models based on their far-infrared and radio emission. The still unexplained origin of this millimetre excess is investigated here using the Planck data. The integrated SED of the two galaxies before subtraction of the foreground (Milky Way) and background (CMB fluctuations) emission are in good agreement with previous determinations, confirming the presence of the millimetre excess. In the context of this preliminary analysis we do not propose a full multi-component fitting of the data, but instead subtract contributions unrelated to the galaxies and to dust emission. The background CMB contribution is subtracted using an internal linear combination (ILC) method performed locally around the galaxies. The foreground emission from the Milky Way is subtracted as a Galactic H i template, and the dust emissivity is derived in a region surrounding the two galaxies and dominated by Milky Way emission. After subtraction, the remaining emission of both galaxies correlates closely with the atomic and molecular gas emission of the LMC and SMC. The millimetre excess in the LMC can be explained by CMB fluctuations, but a significant excess is still present in the SMC SED. The Planck and IRAS-IRIS data at 100 μm are combined to produce thermal dust temperature and optical depth maps of the two galaxies.Corresponding author: J.-P. Bernard, e-mail: jean-philippe.bernard@cesr.frArticle published by EDP Sciences A17, page 1 of 17 A&A 536, A17 (2011) The LMC temperature map shows the presence of a warm inner arm already found with the Spitzer data, but which also shows the existence of a previously unidentified cold outer arm. Several cold regions are found along this arm, some of which are associated with known molecular clouds. The dust optical depth maps are used to constrain the thermal dust emissivity power-law index (β). The average spectral index is found to be consistent with β =1.5 and β =1.2 below 500 μm for the LMC and SMC respectively, significantly flatter than the values observed in the Milky Way. Also, there is evidence in the SMC of a further flattening of the SED in the sub-mm, unlike for the LMC where the SED remains consistent with β =1.5. The spatial distribution of the millimetre dust excess in the SMC follows the gas and thermal dust distribution. Different models are explored in order to fit the dust emission in the SMC. It is concluded that the millimetre excess is unlikely to be caused by very cold dust emission and that it could be due to a combination of spinning dust emission and thermal dust emission by more amorphous dust grains than those present in our Galaxy.

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The Radio Continuum of the Metal‐deficient Blue Compact Dwarf Galaxy SBS 0335−052

Cited by 47 publications

References 56 publications

Probing Star Formation at Low Metallicity: The Radio Emission of Super Star Clusters in SBS 0335–052

Probing Star Formation at Low Metallicity: The Radio Emission of Super Star Clusters in SBS 0335–052

The size-density relation of extragalactic H II regions

Planckearly results. XVII. Origin of the submillimetre excess dust emission in the Magellanic Clouds

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