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arXiv 1406.3574astro-ph.GAastro-ph.CO
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NGC 2865星系星系际介质中H $α$发射体的普查

A census of H$α$ emitters in the intergalactic medium of the NGC 2865 system

F. Urrutia-Viscarra, M. Arnaboldi, C. Mendes de Oliveira, O. Gerhard, S. Torres-Flores, E. R. Carrasco, D. de Mello

摘要:

潮汐碎片富含HI气体,形成于相互作用和合并系统中,是研究星系外恒星形成的合适实验室。最近,几个这样的系统被观测到,其中包含了许多年轻的恒星形成区域的星系外。在以前的工作中,我们已经研究了年轻的恒星形成区域外的星系在不同的系统与光学和/或气体潮汐碎片,所有这些都与可用的档案GALEX/UV图像,以了解他们发生的频率和在哪种类型的环境。在本文中,我们寻找星系NGC 2865周围的恒星形成区,这是一个壳层星系,它被一个环的HI,与总质量为1.2 × 10 $^9$ M $_\odot$。利用双子座望远镜的多狭缝成像光谱技术,我们探测到星系NGC 2865周围的所有H $α$发射源,其通量极限为10 $^{-18}$ erg cm $^{-2}$ s $^{-1}$ erg cm $^{-1}$。再加上近和远紫外光通量信息,我们的特点,这些HII地区的恒星形成率,质量,年龄和金属丰度。我们总共在NGC 2865星系周围HI气体东南尾部的60个$\times$ 60 Kpc场中发现了26个发射线源。在26个H PDMATHAMO发射体中,有19个位于卫星星系FGCE 0745中,7个位于星系际HII区,散布在NGC 2865周围HI气体的南尾。我们发现星系际HII区域很年轻($<$ 200 Myr),恒星质量范围为4 X 10 $^3$ M $_\odot$至17 x 10 $^6$ M $_\odot$。这些都是在低HI气体密度的区域发现的,在那里形成恒星的可能性预计是低的。对于银河系间的HII区域之一,我们估计太阳氧丰度为12 + log(O/H)$\sim$ 8.7。我们还能够估计卫星星系FGCE 0745的金属丰度为12 + log(O/H)~ 8.0。

英文摘要:

Tidal debris which are rich in HI gas, formed in interacting and merging systems, are suitable laboratories to study star formation outside galaxies. Recently, several such systems were observed, which contained many young star forming regions outside the galaxies. In previous works, we have studied young star forming regions outside galaxies in different systems with optical and/or gaseous tidal debris, all of them with available archive GALEX/UV images, in order to understand how often they occur and in which type of environments. In this paper we searched for star forming regions around the galaxy NGC2865, a shell galaxy which is circled by a ring of HI, with a total mass of 1.2 x 10$^9$ M$_\odot$. Using the Multi-Slit Imaging Spectroscopy Technique with the Gemini telescope, we detected all H$α$ emitting sources in the surroundings of the galaxy NGC2865, down to a flux limit of 10$^{-18}$ erg cm$^{-2}$ s$^{-1}$ Å$^{-1}$. Together with Near and Far-Ultraviolet flux information we characterize the star formation rates, masses, ages, and metallicities for these HII regions. In total, we found 26 emission-line sources in a 60 $\times$ 60 Kpc field centered over the southeastern tail of the HI gas present around the galaxy NGC2865. Out of the 26 H$α$ emitters, 19 are in the satellite galaxy FGCE 0745 and seven are intergalactic HII regions scattered over the south tail of the HI gas around NGC2865. We found that the intergalactic HII regions are young ($<$200 Myr) with stellar masses in the range 4 X 10$^3$M$_\odot$ to 17x10$^6$ M$_\odot$. These are found in a region of low HI gas density, where the probability of forming stars is expected to be low. For one of the intergalactic HII regions we estimated a solar oxygen abundance of 12 + log(O/H) $\sim$ 8.7. We also were able to estimate the metallicity for the satellite galaxy FGCE0745 to be 12 + log(O/H) ~ 8.0.

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