An investigation of the origin of He II nebular emission in spectra of low-metallicity H II regions from Sloan Digital Sky Survey
Heading:
| 1Agiienko, KB 1Main Astronomical Observatory of the National Academy of Sciences of Ukraine, Kyiv, Ukraine |
| Kinemat. fiz. nebesnyh tel (Online) 2013, 29(5):25-35 |
| Start Page: Extragalactic Astronomy |
| Language: Russian |
Abstract: We study possible sources of hard ionising radiation in H II regions with low metallicity. The presence of the nebular He II λ 468.6 nm emission line in the H II region spectrum can be considered as an indication of this radiation. While theoretical stellar population synthesis models predict He II emission-line intensities decreasing with the metallicity, the intensity of this line in H II regions from our sample is increasing with metallicity decrease. That is in good agreement with previous studies. Some relation between the He II emission and presence of Wolf — Rayet (WR) stars is discussed. Only 30 % of spectra from our sample show nebular emission superposed with broad He II emission from WR stars. This evidence does not exclude WR stars as a possible source of hard ionising radiation in some H II regions. However, other sources such as fast radiative shocks seem to be more likely. |
| Keywords: Nebular He II, SLOAN |
References:
1.K. N. Abazajian, J. K. Adelman-McCarthy, et al., “The seventh data release of the Sloan Digital Sky Survey,” Astrophys. J., Suppl. Ser. 182, 543–558 (2009).
https://doi.org/10.1088/0067-0049/182/2/543
2.J. A. Baldwin, M. M. Phillips, and R. Terlevich, “Classification parameters for the emission-line spectra of extragalactic objects,” Publ. Astron. Soc. Pac. 93, 5–19 (1981).
https://doi.org/10.1086/130766
3.F. Bresolin, R. C. Kennicutt, and D. R. Garnett, “The ionizing stars of extragalactic H II regions,” Astrophys. J. 510, 104–124 (1999).
https://doi.org/10.1086/306576
4.J. Brinchmann, D. Kunth, and F. Durret, “Galaxies with Wolf-Rayet signatures in the low-redshift Universe. A survey using the Sloan Digital Sky Survey,” Astron. Astrophys. 485, 657–677 (2008).
https://doi.org/10.1051/0004-6361:200809783
5.P. A. Crowther, “Physical properties of Wolf-Rayet stars,” Annu. Rev. Astron. Astrophys. 45, 177–219 (2007).
https://doi.org/10.1146/annurev.astro.45.051806.110615
6.P. A. Crowther and L. J. Hadfield, “Reduced Wolf-Rayet line luminosities at low metallicity,” Astron. Astrophys. 449, 711–722 (2006).
https://doi.org/10.1051/0004-6361:20054298
7.G. J. Ferland, K. T. Korista, D. A. Verner, et al., “CLOUDY 90: numerical simulation of plasmas and their spectra,” Publ. Astron. Soc. Pac. 110, 761–779 (1998).
https://doi.org/10.1086/316190
8.D. R. Garnett, “Electron temperature variations and the measurement of nebular abundances,” Astron. J. 103, 1330–1337 (1992).
https://doi.org/10.1086/116146
9.N. G. Guseva, Yu. I. Izotov, and T. X. Thuan, “A spectroscopic study of a large sample of Wolf-Rayet galaxies,” Astrophys. J. 531, 776–803 (2000).
https://doi.org/10.1086/308489
10.L. J. Hadfield and P. A. Crowther, “A survey of the Wolf-Rayet population of the barred, spiral galaxy NGC 1313,” Mon. Not. R. Astron. Soc. 381, 418–432 (2007).
https://doi.org/10.1111/j.1365-2966.2007.12284.x
11.Yu. I. Izotov, D. Schaerer, A. Blecha, et al., “VLT/GIRAFFE spectroscopic observations of the metal-poor blue compact dwarf galaxy SBS 0335-052E,” Astron. Astrophys. 459, 71–84 (2006).
https://doi.org/10.1051/0004-6361:20065622
12.Yu. I. Izotov, G. Stasinska, G. Meynet, et al., “The chemical composition of metal-poor emission-line galaxies in the Data Release 3 of the Sloan Digital Sky Survey,” Astron. Astrophys. 448, 955–970 (2006).
https://doi.org/10.1051/0004-6361:20053763
13.Yu. I. Izotov and T. X. Thuan, “Deep Hubble Space Telescope ACS observations of IZw 18: a young galaxy in formation,” Astrophys. J. 616, 768–782 (2004).
https://doi.org/10.1086/424990
14.Yu. I. Izotov, T. X. Thuan, and V. A. Lipovetsky, “The primordial helium abundance from a new sample of metaldeficient blue compact galaxies,” Astrophys. J. 435, 647–667 (1994).
https://doi.org/10.1086/174843
15.Yu. I. Izotov, T. X. Thuan, and G. Privon, “The detection of [Ne V] emission in five blue compact dwarf galaxies,” Mon. Not. R. Astron. Soc. 427, 1229–1237 (2012).
https://doi.org/10.1111/j.1365-2966.2012.22051.x
16.G. Kauffmann, T. M. Heckman, C. Tremonti, et al., “The host galaxies of active galactic nuclei,” Mon. Not. R. Astron. Soc. 346, 1055–1077 (2003).
https://doi.org/10.1111/j.1365-2966.2003.07154.x
17.C. Kehrig, M. S. Oey, P. A. Crowther, et al., “Gemini GMOS spectroscopy of He II nebulae in M 33,” Astron. Astrophys. 526, A128 (2011).
https://doi.org/10.1051/0004-6361/201015493
18.C. Leitherer, D. Schaerer, J. D. Goldader, et al., “Starburst99: synthesis models for galaxies with active star formation,” Astrophys. J., Suppl. Ser. 123, 3–40 (1999).
https://doi.org/10.1086/313233
19.A. Maeder and P. Conti, “Massive star populations in nearby galaxies,” Annu. Rev. Astron. Astrophys. 32, 227–275 (1994).
https://doi.org/10.1146/annurev.aa.32.090194.001303
20.G. Meynet and A. Maeder, “Stellar evolution with rotation. XI. Wolf-Rayet star populations at different metallicities,” Astron. Astrophys. 429, 581–598 (2005).
https://doi.org/10.1051/0004-6361:20047106
21.K. F. Neugent and P. Massey, “The Wolf-Rayet content of M33,” Astrophys. J. 733, A123 (2011).
https://doi.org/10.1088/0004-637X/733/2/123
22.L. S. Pilyugin and L. Mattsson, “Abundance determination in H II regions from spectra without the [O II] λ3727 + λ3729 line,” Mon. Not. R. Astron. Soc. 412, 1145–1150 (2011).
23.D. Schaerer, “On the properties of massive Population III stars and metal-free stellar populations,” Astron. Astrophys. 382, 28–42 (2002).
https://doi.org/10.1051/0004-6361:20011619
24.D. Schaerer, “The transition from Population III to normal galaxies: Lyα and He II emission and the ionizing properties of high redshift starburst galaxies,” Astron. Astrophys. 397, 527–538 (2003).
https://doi.org/10.1051/0004-6361:20021525
25.D. Schaerer, T. Contini, D. Kunth, and G. Meynet, “Detection of Wolf-Rayet stars of WN and WC subtypes in super-star clusters of NGC 5253,” Astrophys. J., Lett. 481, L75–L79 (1997).
https://doi.org/10.1086/310659
26.D. Schaerer and W. D. Vacca, “New models for Wolf-Rayet and O populations in young starbursts,” Astrophys. J. 497, 618–644 (1998).
https://doi.org/10.1086/305487
27.M. Shirazi and J. Brinchmann, “Strongly star forming galaxies in the local Universe with nebular He II 4686 Emission,” Mon. Not. R. Astron. Soc. 421, 1043–1063 (2012).
https://doi.org/10.1111/j.1365-2966.2012.20439.x
28.G. Stasinska and Yu. I. Izotov, “Modeling the emission line sequence of H II galaxies,” Astron. Astrophys. 397, 71–85 (2003).
https://doi.org/10.1051/0004-6361:20021510
29.T. X. Thuan and Yu. I. Izotov, “High-Ionization emission in metal-deficient blue compact dwarf galaxies,” Astrophys. J., Suppl. Ser. 161, 240–270 (2005).
https://doi.org/10.1086/491657
30.A. E. Whitford, “The law of interstellar reddening,” Astron. J. 63, 201–207 (1958).
https://doi.org/10.1086/107725