赛弗特星系恒星速度弥散度的测量

星系中心黑洞质量和核球恒星速度弥散度的紧密关系揭示出准确测量恒星速度弥散度对测定星系中心黑洞质量尤为重要.文中提供了一种利用SDSS(Sloan Digital SkySurvey)光谱测定速度弥散度及其不确定性的方法.通过对像素空间包含显著特征吸收线的4个不同谱区的拟合,得到准确测量恒星速度弥散度σ的光谱区域.文中4个拟合波段主要包含的吸收线为CaⅡK,MgⅠb三重线(波长5167.5,5172.7,5183.6(?))和CaT(CaⅡ三重线,波长8498.0,8542.1,8662.1(?)).不同区域结果表明,MgⅠb区由于受到铁族发射线影响,拟合的σ值偏低;CaⅡK线区谱线强度很弱,易受限于最小二乘法搜索算法;CaT+CaⅡK联合区得出的速度弥散度和只计算CaT区域的结果相当.利用该方法,测试了一个红移小于0.05的赛弗特星系样本,发现CaT区是测速度弥散度的最佳谱区.

Measuring the Stellar Velocity Dispersion in Seyfert Galaxies

The tight relation between the black hole mass and the stellar velocity dis-persion indicates that the velocity dispersion is an important parameter to estimate the black hole mass.A new method is proposed in this paper to measure the stellar velocity dispersion and its uncertainty for a sample of Seyfert galaxies from Sloan Digital Sky Survey(SDSS).Through fitting four spectral regions which contain stellar absorption features in pixel domain including the Ca Ⅱ K,Mg Ⅰ b triplet and Ca Ⅱ triplet absorption lines,we determine a better spectral region to measure the stellar velocity dispersion.The results show a significant difference:the values obtained in Mg Ⅰ b region are smaller due to the contamination from the broad Fe Ⅱ emission lines;the velocity dispersion is easily biased by the searching algorithm in Ca Ⅱ K region because of the weakness of lines;and similar results are derived in Ca Ⅱ K+Ca Ⅱ triplet and Ca Ⅱ K regions.For the Seyfert galaxies with z < 0.05,we conclude that Ca Ⅱ triplet is the best choice to measure the stellar velocity dispersion.