Study On HeⅠ~* Absorption-line Systems In Quasars

Helium is the second most abundant element in the universe, yet in the literaturethere are only 7 quasars which show HeⅠ~* absorption systems in their spectra. Usinglocally weighted scatterplot smoothing method, we identify 202 HeⅠ~* absorption-linequasars out of 105783 SDSS DR7 quasars. This increases the current sample size of HeⅠ~* absorption-line quasars by over an order of magnitude. There are high occurrencerates of both HeⅠ~* and Balmer absorptions or both HeⅠ~* and FeⅡ~* absorptions in oneobject. We find that 21 quasars show HeⅠ~* and Balmer absorptions at the same time,while 31 quasars show HeⅠ~* and FeⅡ~* absorptions at the same time.From study on two individual quasars which show HeⅠ~* and Balmer absorption,namely, LBQS 1206+1052 SDSS J2220+0109, we find that the absorption gasesare stratified. HeⅠ~* absorptions arise in ionized HⅡregion, while Balmer absorptionlines arise in partially ionized region behind the ionized one. Collisional excitation withLyαscattering is the main mechanism responsible for Balmer absorption. Typically,ahydrogen column density of NH～1021–1022is needed to generate observed Balmerabsorption at a density of ne～106–108cm 3the column is proportional to ne 0.5.In the spectrum of narrow-line quasar SDSS J0802+5513, the absorptions covera velocity range of -900–1000 km s 1. The width of MgⅡabsorption lines is 2500km s 1, which put the object into the regime of low ionized broad absorption-linequasars (LoBALs). .The object is heavily reddened, with an E(B-V) of 0.36. From themetastable FeⅡ~* absorption lines, we get that the electron density neis about 8×103cm 3. Line blendings in this object make the line measurements quite uncertain, so wefurtherstudythespectrumofSDSSJ2226+1427, whichshownarrowerabsorptionlinesinHeⅠ~*, FeⅡ~* MnⅡ,NiⅡ,ZnⅡ,MgI,MgⅡ,AlⅡ,AlⅡI,SiⅡ.Theabsorptionlinesare blueshifted by 320 km s 1and with an FWHM of 250 km s 1. Narrower absorptionline widths make the measurements quite reliable, we get an ne= 2×103cm 3for theabsorption gas. Combining above results with photoionization calculations, we inferthat the absorption gases in both objects are on the scale of kpc.Study on individuals shows that the HeⅠand FeⅡ~* absorption line systems arequite large-scale. 31 such sources with FeⅡabsorption in our sample can help us con-firm the results from individuals and explore the full parameter space of HeⅠ~* and FeⅡ~* absorption line region.Furthermore, we study the multi-band properties of the 202 HeⅠ~* absorption line quasars. We find that, compared to normal quasars, HeⅠ~* absorption line quasars showredder color, with a (g-i) distribution peaking at 0.4; they are barely detected inX-ray band, with a RASS detection rate of 3% they have a high detection rate inradio band, with a FIRST detection rate of 21% most of the objects with radio SEDmeasurement show steep spectrum. These results suggest that the absorption gas inHeⅠ~* absorption line quasars is dusty and the gas's column density is relatively large.