Emission spectrum of ionized gas in the irregular galaxy Holmberg II

Egorov, Oleg V.; Lozinskaya, T. A.; Моисеев, А. В.

doi:10.1093/mnras/sts428

Cited by 20 publications

(24 citation statements)

References 47 publications

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“…In Holmberg II data on the [O ii]λλ3727, 3729 lines are not available except for a couple of complexes, so we rely on the 'NS' calibration (Pilyugin & Mattsson 2011) to estimate metallicities in this galaxy. These two calibrations are close to each other as shown in the work of Egorov, Lozinskaya & Moiseev (2013). We compared the NS and ONS metallicity estimates for the rest of our sample of H ii complexes and found them to be consistent with each other.…”

Section: Metallicitiessupporting

confidence: 84%

Optical and infrared emission of H ii complexes as a clue to the PAH life cycle

Khramtsova¹,

Wiebe²,

Lozinskaya³

et al. 2014

Monthly Notices of the Royal Astronomical Society

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We present an analysis of optical spectroscopy and infrared aperture photometry of more than 100 H ii complexes in nine galaxies. Spectra obtained with the 6-m telescope of SAO RAS are used along with archival data from Spitzer and several ground-based telescopes to infer a strength of polycyclic aromatic hydrocarbon (PAH) emission, age, properties of the UV radiation field, and metallicity of studied H ii complexes. Physical properties (age, radiation field parameters, metallicity) are related to the F 8 /F 24 ratio used as a proxy for the PAH abundance in order to reveal factors that may influence the PAH evolution in H ii complexes. The well-known correlation between the F 8 /F 24 ratio and metallicity is confirmed in the studied complexes. The infrared flux ratio also correlates with the [O iii]λ5007/Hβ ratio which is often considered as an indicator of the radiation field hardness, but this correlation seems to be a mere reflection of a correlation between [O iii]λ5007/Hβ and metallicity. In separate metallicity bins, the F 8 /F 24 ratio is found to correlate with an age of an H ii complex, which is estimated from the equivalent width of Hβ line. The correlation is positive for low metallicity complexes and negative for high metallicity complexes. Analysing various mechanisms of PAH formation and destruction in the context of found correlations, we suggest that PAH abundance is likely altered by the UV radiation within H ii complexes, but this is not necessarily due to their destruction. If PAHs can also form in H ii complexes due to some processes like aromatisation, photodestruction, shattering and sputtering of very small grains, the net F 8 /F 24 ratio is determined by a balance between all these processes that can be different at different metallicities.

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Section: Metallicitiessupporting

confidence: 84%

Optical and infrared emission of H ii complexes as a clue to the PAH life cycle

Khramtsova¹,

Wiebe²,

Lozinskaya³

et al. 2014

Monthly Notices of the Royal Astronomical Society

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“…The top and bottom images correspond to the same area with different contrast. White circle shows the area of He ii 4686 Å emission detected in Egorov et al (2013).…”

Section: Morphology and Ionization Budget Of Star Formation Complexesmentioning

confidence: 99%

“…Hong et al (2013) All the used line ratios were corrected by reddening using the mean value E(B − V ) = 0.05 (Egorov et al 2013). We calculated the values of Hβ fluxes from the Hα flux using the theoretical ratio I(Hα)/I(Hβ) for T = 10000 K (Osterbrock & Ferland 2006).…”

Section: Search For Snrs In the Sgsmentioning

confidence: 99%

Complexes of triggered star formation in supergiant shell of Holmberg II

Egorov

Lozinskaya

Моисеев

et al. 2016

Mon. Not. R. Astron. Soc.

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We report a detailed analysis of all regions of current star formation in the walls of the supergiant H i shell (SGS) in the galaxy Holmberg II based on observations with a scanning Fabry-Perot interferometer at the 6-m SAO RAS telescope. We compare the structure and kinematics of ionized gas with that of atomic hydrogen and with the stellar population of the SGS. Our deep Hα images and archival images taken by the HST demonstrate that current star formation episodes are larger and more complicated than previously thought: they represent unified star-forming complexes with sizes of several hundred pc rather than 'chains' of separate bright nebulae in the walls of the SGS. The fact that we are dealing with unified complexes is evidenced by identified faint shell-like structures of ionized and neutral gas which connect several distinct bright H ii regions. Formation of such complexes is due to the feedback of stars with very inhomogeneous ambient gas in the walls of the SGS. The arguments supporting an idea about the triggering of star formation in SGS by the H i supershells collision are presented. We also found a faint ionized supershell inside the H i SGS expanding with a velocity of no greater than 10 − 15 km s −1 . Five OB stars located inside the inner supershell are sufficient to account for its radiation, although a possibility of leakage of ionizing photons from bright H ii regions is not ruled out as well.

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“…The metallicity of the system is a key issue relevant to the absence of strong jet lines in Holmberg II X-1. The dwarf galaxy Holmberg II appears to have a sub-solar metallicity in general, with an estimated metalicity of ∼0.2 Z ⊙ (Egorov et al 2013). A low metallicity could help hide any line emission.…”

Section: The Hard Excessmentioning

confidence: 99%

NUSTAR,XMM-NEWTON, ANDSUZAKUOBSERVATIONS OF THE ULTRALUMINOUS X-RAY SOURCE HOLMBERG II X-1

Walton

Middleton

Rana

et al. 2015

ApJ

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We present the first broadband 0.3-25.0 keV X-ray observations of the bright ultraluminous X-ray source (ULX) Holmberg II X-1, performed by NuSTAR, XMM-Newton, and Suzaku in 2013 September. The NuSTAR data provide the first observations of Holmberg II X-1 above 10 keV and reveal a very steep high-energy spectrum, similar to other ULXs observed by NuSTAR to date. These observations further demonstrate that ULXs exhibit spectral states that are not typically seen in Galactic black hole binaries. Comparison with other sources implies that Holmberg II X-1 accretes at a high fraction of its Eddington accretion rate and possibly exceeds it. The soft Xray spectrum (E 10 < keV) appears to be dominated by two blackbody-like emission components, the hotter of which may be associated with an accretion disk. However, all simple disk models under-predict the NuSTAR data above ∼10 keV and require an additional emission component at the highest energies probed, implying the NuSTAR data does not fall away with a Wien spectrum. We investigate physical origins for such an additional high-energy emission component and favor a scenario in which the excess arises from Compton scattering in a hot corona of electrons with some properties similar to the very high state seen in Galactic binaries. The observed broadband 0.3-25.0 keV luminosity inferred from these epochs is L (8.1 0.1) 10 X 39 = ± × erg s −1 , typical for Holmberg II X-1, with the majority of this flux (∼90%) emitted below 10 keV.

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Emission spectrum of ionized gas in the irregular galaxy Holmberg II

Cited by 20 publications

References 47 publications

Optical and infrared emission of H ii complexes as a clue to the PAH life cycle

Optical and infrared emission of H ii complexes as a clue to the PAH life cycle

Complexes of triggered star formation in supergiant shell of Holmberg II

NUSTAR,XMM-NEWTON, ANDSUZAKUOBSERVATIONS OF THE ULTRALUMINOUS X-RAY SOURCE HOLMBERG II X-1

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