The Nature of Radio Continuum Emission in the Dwarf Starburst Galaxy NGC 625

Cannon, John; Skillman, Evan D.

doi:10.1086/421903

Cited by 23 publications

(27 citation statements)

References 39 publications

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“…NGC 604 and 30 Doradus in the Large Magellanic Cloud), and are also extended in the radio, with diameters of a few hundred pc. The clusters are similar in number and size to those in NGC 625, another, higher-metallicity, BCD (1/6 Z , Cannon & Skillman 2004).…”

Section: The Starburstmentioning

confidence: 59%

“…Such misalignment of radio peaks and star clusters has been attributed to the effects of feedback (e.g., Cannon & Skillman 2004), in which the star cluster has swept out its immediate surroundings (Johnson et al 2003). While the thermal radio emission traces the ongoing star formation, possibly hidden by dust, the non-thermal emission probes past regions of star formation, through the synchrotron radiation of SNe cavities.…”

Section: The Windblown Superbubble and Feedbackmentioning

confidence: 99%

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The radio continuum of the extremely metal-poor blue compact dwarf galaxy I Zw 18

Hunt

Dyer

Thuan

2005

A&A

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Abstract. We present 1.4, 4.8 and 8.4 GHz Very Large Array observations of the lowest metallicity blue compact dwarf (BCD) galaxy known, I Zw 18, with a heavy element abundance of ∼2% that of the Sun. The 1.4 and 4.8 GHz images reveal a halo of mostly non-thermal extended emission, with asymmetric lobes extending laterally in the east-west direction. We interpret the radio halo as produced by a superbubble carved out in the interstellar medium (ISM) by supernovae, with a bipolar outflow oriented along the galaxy's rotation axis. The overall spectral index is −0.39 from 1.4 Ghz to 4.8 Ghz and −0.13 from 4.8 to 8.4 GHz. The radio luminosity of I Zw 18 has a thermal to total emission fraction of 0.30 at 1.4 GHz. This fraction increases to 0.41 at 4.8 GHz and to 0.47 at 8.4 GHz. The thermal radio luminosity gives a total of 1200 O7 V stars and a star formation rate of 0.1 M yr −1 . Unlike the BCD SBS 0335−052 which has a similar metallicity and forms stars with a high rate in regions which are dense and compact, I Zw 18 makes stars at a smaller rate in complexes which are diffuse and extended. Star formation in BCDs thus appears to occur in a bimodal fashion, independently of the metallicity of the interstellar medium.Key words. galaxies: dwarf -galaxies: starburst -galaxies: star clusters -radio continuum: galaxiesradio continuum: ISM -ISM: supernova remnants IntroductionHow and when galaxies formed is a fundamental problem of modern astrophysics. To date however the quest for truly young galaxies in the process of forming at redshifts >5-6 is still unsuccessful. The high-redshift objects discovered so far are typically enriched in heavy elements, implying that the starformation events which formed them took place in an earlier yet unobserved epoch. Instead of looking for young systems at high redshifts, an alternative approach is to study star formation in environments which are similar to primordial ones, in that they are unevolved chemically. Chemically unenriched interstellar media in the local universe, such as those in metalpoor blue compact dwarf galaxies (BCDs), approximate the best those which hosted primordial starbursts; but because they are nearby, they are easier to study than the high-redshift Lyα absorption systems. Therefore, low-metallicity BCDs may be useful "templates" for studying how the first stars and galaxies formed.Because of its extremely low metal abundance, I Zw 18 is arguably one of the best nearby BCDs with which to study primordial-like starbursts. First discovered by Zwicky (1966), I Zw 18 was originally described as a double system of compact galaxies, which are instead two massive star clusters, the brighter northwest (NW) and fainter southeast (SE) components, separated by ∼300 pc. The galaxy, together with a starforming region ∼1.3 kpc to the NW (component C), is embedded within a massive H cloud (van Zee et al. 1998).I Zw 18 has the lowest metal abundance (∼1/50 Z Izotov et al. 2001, and references therein) of known star-forming systems in the local universe. Very metal-deficie...

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Section: The Starburstmentioning

confidence: 59%

Section: The Windblown Superbubble and Feedbackmentioning

confidence: 99%

The radio continuum of the extremely metal-poor blue compact dwarf galaxy I Zw 18

Hunt

Dyer

Thuan

2005

A&A

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“…In this sense, the observed sizedensity relation of extragalactic H ii regions can be taken as an age sequence, although the relation contains different populations starting from different initial densities. The extreme youth of "super-active" (extremely dense) regions is also supported by the typical rising thermal radio spectrum from free-free gas absorption (Cannon & Skillman 2004; HH06; HH06 also argue that the initial density is important for the rising spectrum).…”

Section: Summary Of the Evolutionary Tracksmentioning

confidence: 93%

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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“…Total infrared luminosities L TIR are taken from Madden et al (2013), as determined from Spitzer bands using the prescriptions in Dale & Helou (2002). Radio continuum measurements are retrieved from the NRAO VLA Sky Survey (NVSS) catalog (Condon et al 1998), Cannon & Skillman (2004), Thuan et al (2004), andHunt et al (2005). The emission from PAHs usually dominates the IRAC 8 µm band in metal-rich galaxies.…”

Section: A3 Comparison Of Obscured Sfr Tracers: Irac8 µMmentioning

confidence: 99%

The applicability of far-infrared fine-structure lines as star formation rate tracers over wide ranges of metallicities and galaxy types

Looze

Cormier

Lebouteiller

et al. 2014

A&A

382

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Aims. We analyze the applicability of far-infrared fine-structure lines [C] 158 µm, [O] 63 µm, and [O] 88 µm to reliably trace the star formation rate (SFR) in a sample of low-metallicity dwarf galaxies from the Herschel Dwarf Galaxy Survey and, furthermore, extend the analysis to a broad sample of galaxies of various types and metallicities in the literature. Methods. We study the trends and scatter in the relation between the SFR (as traced by GALEX FUV and MIPS 24 µm) and farinfrared line emission, on spatially resolved and global galaxy scales, in dwarf galaxies. We assemble far-infrared line measurements from the literature and infer whether the far-infrared lines can probe the SFR (as traced by the total infrared luminosity) in a variety of galaxy populations. Results. In metal-poor dwarfs, the [O] 63 and [O] 88 lines show the strongest correlation with the SFR with an uncertainty on the SFR estimates better than a factor of 2, while the link between [C] emission and the SFR is more dispersed (uncertainty factor of 2.6). The increased scatter in the SFR-L [CII] relation toward low metal abundances, warm dust temperatures, and large filling factors of diffuse, highly ionized gas suggests that other cooling lines start to dominate depending on the density and ionization state of the gas. For the literature sample, we evaluate the correlations for a number of different galaxy populations. The [C] and [O] 63 lines are considered to be reliable SFR tracers in starburst galaxies, recovering the star formation activity within an uncertainty of factor 2. For sources with composite and active galactic nucleus (AGN) classifications, all three FIR lines can recover the SFR with an uncertainty factor of 2.3. The SFR calibrations for ultra-luminous infrared galaxies (ULIRGs) are similar to starbursts/AGNs in terms of scatter but offset from the starburst/AGN SFR relations because of line deficits relative to their total infrared luminosity. While the number of detections of the FIR fine-structure lines is still very limited at high redshift for [O]

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The Nature of Radio Continuum Emission in the Dwarf Starburst Galaxy NGC 625

Cited by 23 publications

References 39 publications

The radio continuum of the extremely metal-poor blue compact dwarf galaxy I Zw 18

The radio continuum of the extremely metal-poor blue compact dwarf galaxy I Zw 18

The size-density relation of extragalactic H II regions

The applicability of far-infrared fine-structure lines as star formation rate tracers over wide ranges of metallicities and galaxy types

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