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arXiv 1311.2192astro-ph.GA
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蓝色致密矮星系Mrk 996的物理条件和运动学的Gemini/GMOS研究

A Gemini/GMOS study of the physical conditions and kinematics of the blue compact dwarf galaxy Mrk 996

Eduardo Telles, Trinh X. Thuan, Yuri I. Izotov, Eleazar Rodrigo Carrasco

摘要:

利用双子座多目标摄谱仪(GMOS)对不寻常的蓝矮星系Mrk 996进行了积分场光谱研究。我们通过速度和色散图,发射线强度和比率图,并通过一种新的电子密度极限成像技术,在Mrk 996中的不同区域的电离特性与它们的运动学性质相关。从地图上,我们可以在空间上区分一个非常密集的高电离区与宽线的核区域,和一个不太密集的低电离区与窄线的环核区域。在Mrk 996的综合光谱中发现了四个运动学上不同的线系统,这表明沃尔夫-拉叶星(WR)在核区域的恒星风外流,叠加在一个基本的旋转模式上。从蓝色和红色凸起的强度,我们得出了$\sim$ 473晚氮(WNL)星和$\sim$ 98早碳(WCE)星的人口在Mrk 996的核心,导致高N(WR)/N(O+WR)为0.19。我们推导出,对于外部窄线区域,氧丰度12+log(O/H)=7.94 $\pm$ 0.30($\sim$ 0.2 Z $_\odot$)通过使用直接T $_e$方法从检测到的窄[OIII] $λ$ 4363线。然而,Mrk 996的核是氮增强的$\sim$ 20倍,与先前的云模型一致。这种氮的增强可能是由于富氮WR喷出物,但也提高了氮线排放在高密度环境。虽然我们在这里使用了两种新的方法-主成分分析(PCA)层析成像和一种用于映射低密度和高密度云的方法-来分析我们的数据,但需要新的方法来进一步利用丰富的信息。

英文摘要:

We present an integral field spectroscopic study with the Gemini Multi-Object Spectrograph (GMOS) of the unusual blue compact dwarf (BCD) galaxy Mrk 996. We show through velocity and dispersion maps, emission-line intensity and ratio maps, and by a new technique of electron density limit imaging that the ionization properties of different regions in Mrk 996 are correlated with their kinematic properties. From the maps, we can spatially distinguish a very dense high-ionization zone with broad lines in the nuclear region, and a less dense low-ionization zone with narrow lines in the circumnuclear region. Four kinematically distinct systems of lines are identified in the integrated spectrum of Mrk 996, suggesting stellar wind outflows from a population of Wolf-Rayet (WR) stars in the nuclear region, superposed on an underlying rotation pattern. From the intensities of the blue and red bumps, we derive a population of $\sim$473 late nitrogen (WNL) stars and $\sim$98 early carbon (WCE) stars in the nucleus of Mrk 996, resulting in a high N(WR)/N(O+WR) of 0.19. We derive, for the outer narrow-line region, an oxygen abundance 12+log(O/H)=7.94$\pm$0.30 ($\sim$ 0.2 Z$_\odot$) by using the direct T$_e$ method derived from the detected narrow [OIII]$λ$4363 line. The nucleus of Mrk 996 is, however, nitrogen-enhanced by a factor of $\sim$20, in agreement with previous CLOUDY modeling. This nitrogen enhancement is probably due to nitrogen-enriched WR ejecta, but also to enhanced nitrogen line emission in a high-density environment. Although we have made use here of two new methods - Principal Component Analysis (PCA) tomography and a method for mapping low- and high-density clouds - to analyze our data, new methodology is needed to further exploit the wealth of information.

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