Deep spectroscopy of the low-metallicity blue compact dwarf galaxy SBS 0335-052

Izotov, Y. I.; Chaffee, F. H.; Schaerer, D.

doi:10.1051/0004-6361:20011265

Cited by 52 publications

(84 citation statements)

References 14 publications

(23 reference statements)

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“…While the latter is strongest at the location of SSC 1, the former is offset in the direction of SSCs 4 and 5. This feature has been noted before by Izotov et al (1997aIzotov et al ( , 2001b. This is consistent with the idea that the extended He ii k4686 emission is due mainly to the ionizing radiation from radiative shocks, in contrast to the [O iii] k5007 emission, which originates mainly from the ionizing radiation of main-sequence stars.…”

Section: The Decoupling Of the Very Hard And Moderate Ionizing Radiatsupporting

confidence: 91%

“…Several high-ionization emission lines are seen in its spectrum. In addition to the [Fe v] k4227 emission line already discussed by Fricke et al (2001) and Izotov et al (2001b) . This discovery confirms and strengthens the finding by Izotov et al (2001b), who discovered [Fe vi]-[Fe vii] emission in SBS 0335À052E and concluded that ionizing radiation above $7 ryd must be intense in this galaxy.…”

Section: Mmt Observations and Data Reductionmentioning

confidence: 61%

“…The presence of this line, just as that of the He ii k4686 line, requires ionizing radiation with photon energies in excess of 4 ryd. More impressively, Izotov et al (2001b) …”

Section: Introductionmentioning

confidence: 98%

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High‐Ionization Emission in Metal‐deficient Blue Compact Dwarf Galaxies

Thuan

Izotov

2005

ASTROPHYS J SUPPL S

174

193

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Primordial stars are expected to be very massive and hot, producing copious amounts of hard ionizing radiation. The best place to study hard ionizing radiation in the local universe is in very metal-deficient blue compact dwarf (BCD) galaxies. We have carried out a MMT spectroscopic search for [Ne v] k3426 (ionization potential of 7.1 ryd), [Fe v] k4227 (ionization potential of 4 ryd), and He ii k4686 (ionization potential of 4 ryd) emission in a sample of 18 BCDs. We have added data from previous work and from the Data Release 3 of the Sloan Digital Sky Survey. In total, we have assembled a BCD high-ionization sample with [Ne v] emission in four galaxies, [Fe v] emission in 15 galaxies, and He ii emission in 465 galaxies. With this large sample, we have reached the following conclusions. There is a general trend of higher [Ne v], [Fe v], and He ii emission at lower metallicities. However, metallicity is not the only factor that controls the hardness of the radiation. High-mass X-ray binaries and main-sequence stars are probably excluded as the main sources of the very hard ionizing radiation responsible for [Ne v] emission. The most likely source of [Ne v] emission is probably fast radiative shocks moving with velocities k450 km s À1 through a dense interstellar medium with an electron number density of several hundreds cm À3 and associated with supernova explosions of the most massive stars. These have masses of $50-100 M and are formed in very compact super-star clusters (SSCs). The softer ionizing radiation required for He ii emission is likely associated with less massive evolved stars and/or radiative shocks moving through a less dense interstellar medium.

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Section: The Decoupling Of the Very Hard And Moderate Ionizing Radiatsupporting

confidence: 91%

Section: Mmt Observations and Data Reductionmentioning

confidence: 61%

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High‐Ionization Emission in Metal‐deficient Blue Compact Dwarf Galaxies

Thuan

Izotov

2005

ASTROPHYS J SUPPL S

174

193

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“…It was discovered in the Second Byurakan Survey by Izotov et al (1990) who noted its particularly low oxygen abundance of ∼12 + log(O/H) = 7.3, confirmed by subsequent studies (Melnick et al 1992;Izotov et al 2001). SBS 0335−052 is the most metal-poor galaxy known with an SFR ∼ 1 M yr −1 , 20 times higher than in I Zw 18 (Fanelli et al 1988;Hunt et al 2005b).…”

Section: Introductionmentioning

confidence: 87%

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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“…Morphological analogs to I Zw 18 may also exist among compact high-SSFR galaxies at intermediate redshift (0.1 < ∼ z < ∼ 0.8), such as compact narrow emissionline galaxies (Koo et al 1994;Guzmán et al 1998), luminous compact blue galaxies (Guzmán et al 2003;Puech et al 2006) and green pea (GP) galaxies (Cardamone et al 2009;Amorín et al 2010;Izotov et al 2011). The rest-frame EWs of GPs can in some cases almost compete with those of nearby XBCDs (see e.g., Izotov et al 2001b;Papaderos et al 2006b). …”

Section: Zw 18 As Local Morphological Template For Rapidly Assemblimentioning

confidence: 99%

I Zw 18 as morphological paradigm for rapidly assembling high-zgalaxies

Papaderos

Östlin

2012

A&A

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Context. I Zw 18, ever since regarded as the prototypical blue compact dwarf (BCD) galaxy, is, quite ironically, the most atypical BCD known. This is because its large low-surface brightness (LSB) envelope is not due to an old underlying stellar host, as invariably is the case for typical BCDs, but is entirely due to extended nebular emission. Aims. Our goal is to explore I Zw 18 and its detached C component I Zw 18 C down to an unprecedently faint surface brightness μ (mag/ ) level in order to gain further insight into the structural properties and evolutionary history of this enigmatic galaxy pair. Methods. We present a photometric analysis of the entire set of archival HST ACS V, R and I band data for I Zw 18. Results. Radial color profiles for I Zw 18 C reveal blue and practically constant colors (0 ± 0.05) down to μ ∼ 27.6, and a previously undisclosed, slightly redder (V − I ≈ 0.2), stellar population in its extreme periphery (μ ∼ 29). We argue that stellar diffusion over τ ∼ 10 8 yr and the associated stellar mass filtering effect can consistently account for the observed properties of the stellar component in the outskirts of I Zw 18 C. This process, in combination with propagating star formation with a mean velocity of ∼20 km s −1 can reproduce all essential characteristics of I Zw 18 C within ∼τ. An extremely faint substrate of older stars cannot be ruled out but does not need to be postulated. As for I Zw 18, we find that nebular emission (ne) extends out to ∼16 stellar scale lengths, shows a nearly exponential outer profile, and provides at least one third of the total optical emission. Nebular emission dominates already at μ ∼ 23.5, as evident from e.g. the uniform and extremely blue (V − I ≈ -1, R − I ≈ -1.4) colors of the LSB envelope of I Zw 18. Conclusions. The case of I Zw 18 suggests caution in studies of distant galaxies in dominant stages of their evolution, rapidly assembling their stellar mass at high specific star formation rates (SSFRs). It calls attention to the fact of ne not necessarily being cospatial with the underlying ionizing and non-ionizing stellar background. It also does not have to scale with the background surface density. The prodigious energetic output during dominant phases of galaxy evolution may result in large exponential ne envelopes, extending much beyond the still compact stellar component, just like in I Zw 18. Therefore, the morphological paradigm of I Zw 18, while probably unique in the nearby Universe, may be ubiquitous among high-SSFR galaxies at high redshift. Using I Zw 18 as reference, we show that extended ne may introduce substantial observational biases and affect several of the commonly studied fundamental galaxy relations. Among others, we show that the surface brightness profiles of distant morphological analogs to I Zw 18 may be barely distinguishable from Sérsic profiles with an exponent 2 < ∼ η < ∼ 5, thus mimicking the profiles of massive galaxy spheroids.

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Deep spectroscopy of the low-metallicity blue compact dwarf galaxy SBS 0335-052

Cited by 52 publications

References 14 publications

High‐Ionization Emission in Metal‐deficient Blue Compact Dwarf Galaxies

High‐Ionization Emission in Metal‐deficient Blue Compact Dwarf Galaxies

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

I Zw 18 as morphological paradigm for rapidly assembling high-zgalaxies

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