Study and Analysis of Absorption Spectra of Quasars
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1 Study and Analysis of Absorption Spectra of Quasars Bushra Q. AL-Abudi 1 and Nuha S. Fouad 1, University of Baghdad, College of Science, Department of Astronomy and Space, Baghdad-Iraq ABSTRACT A quasi-stellar radio source (quasar) is a very energetic and distant active galactic nucleus. Quasars are extremely luminous and were first identified as being high red shift sources of electromagnetic energy, including radio waves and visible light, that were point-like, similar to stars, rather than extended sources similar to galaxies. The simplest way to explain the quasar's red shifts is to assume that they are extremely distant bodies that follow Hubble's law. In this paper, eight single and four double quasars have been detected from SDSS.The single quasars are: SDSS J , SDSS J ,SDSS J , SDSS J , SDSS J , SDSS J ,SDSS J and SDSS J ,the double quasars are SDSS J , SDSS J , SDSS J and J For both types quasars, chemical composition are determined and the redshift are measured from the absorption spectra, it found that the single quasars spans a redshift range of z the; and double quasars spans a redshift of 1.01 z Applying Hubble's law to these values of redshift, some features of absorption line of quasars are measured and analyzed. Key words: Quasar, Absorption line Spectra, single Quasar; Double Quasars 1. INTRODUCTION Quasars growing supermassive black holes in the centers of massive galaxies are the subset of active galactic nuclei (AGNs) that constitute the most luminous objects in the universe. They radiate substantial power across much of the electromagnetic spectrum, with the source of radiation in each frequency regime originating from a different location with respect to the supermassive black hole. The shape of a quasar s spectral energy distribution (SED) can reveal much about the structure of the black hole-accretion disk system[1].quasars were observed during the first half of the 0th century as radio-sources, but their nature remained unclear for decades. In the late 50s, radio observations revealed that these sources were characterized by very small angular sizes: they were star-like objects, or quasi stellar radio sources, later contracted into quasars. The optical counter-parts of some of these radio sources were observed for the first time in the 60s. Their starlike nature was quickly contradicted by their atypical spectral properties. By 1974, the spectra of over two hundred quasars had been analyzed, and all of them having very large redshifts. The simplest way to explain the quasar s redshifts is to assume that they are extremely distant bodies that follow Hubble s law; in such a way that they are the most distant objects known. Moreover, if the redshifts of quasars are caused by the expansion of the Universe, they are very luminous bodies indeed [, 3]. The quasar absorption lines are crucial to our understanding of the Universe since the absorption lines provide a wealth of information on the gaseous Universe from high redshift to present day. The absorption lines can also allow us to probe them metallicity and ionization state of the gas. Owing to the advent of large spectroscopic surveys such as the Sloan Digital Sky Survey (SDSS), tens of thousands of quasar absorption lines can be identified [4]. In this paper, we will study and analysis the absorption spectra of single and double quasars. This paper is organized as follows. Section presents the features of absorption lines spectra. For each quasar; chemical composition were determined and features of absorption line spectra were measured and analyzed in section 3..Section 4 is devoted to conclusions.. The REDSHIFTS and FEATURES of ABSORPTION LINE SPECTRA The redshift of a quasar is usually denoted by the letter z; that is to say [5]. z (1) 0 where is the shift in wavelength of a spectral line, and 0 is the wavelength that line had when it left the quasar. The redshifts can also be expressed as a velocity by means of the Doppler shift formula. However, if the velocity is small compared to the velocity of light, the following simple form of that formula is normally used. v c () 0 Volume 3, Issue 5, May 014 Page 49
2 v 0 (3) c where v is the velocity, and c the velocity of light. If formula () is converted for the explicit calculation of the redshift Δ formula (3), we can recognize that at a given velocity, the amount of the shift Δ is proportional to the rest wavelength 0 of the corresponding spectral line.the classical method to estimate the distance D is based here on the Hubble s law [6]. v c z H D (4) Where Hubble parameter H (t) is 73 km s -1 Mpc- 1 (t) By converting of formula (4), we get the distance D in (Mpc) c z D (5) H (t) Formula (5) also expresses that the distance D increases proportional to the Redshift z. Given that the quasars have very large redshifts; showing that these objects are moving at relativistic recession velocities; it is necessary to use the exact formula for the relativistic Doppler shift [6]. (1 (1 v c v c ) ) (6) On the other hand, there is another relativistic transformation equation for the volume of the material bodies. Since the transverse dimensions do not change because of the motion, the volume V of a body decreases according to the following formula [6]. v V V 0 1 (7) c Where Vo is the proper volume of the body. It is well known from Optics that the ratio of the image size q, to the object size p is what is called the magnification M; so that, M=q/p. According to the relativistic transformation equation 7, it could be considered that V is the volume image, and Vo is the volume object; in such a way that [6]. v M 1 (8) c And also we can calculate Redshift as lookback Time from the following equation [6]. tn t (9) ( 1 z) 3 Where t n Gyr (i) Also from Redshift we can determine the Post-recombination Density n H using the following equation [6]. n H 1.6 x10-7 (1+z) 3 Cm -3 (10) At recombination (z ~1000): n H ~ 00 cm -3, at reionization (z ~ 7): n H ~ 10-4 cm -3. Also from Redshift we can determine the Atomic Hydrogen Abundance X(H) using the following equation [6]. X(H) = 4Χ10 8 (1+z) 3 << 1 (11) Gunn and Peterson (GP) calculate the observed absorption optical depth from Redshift of Quasar as following equation [6]. Ʈ GP.6Χ10 4 X(H) (1+z) 3/ (1) In this work, We selected eight single quasars and four double quasars from the Sloan Digital Sky Survey (SDSS) to measure the Redshift of quasars [7]. 3. SPECTRAL ANALYSIS of SINGLE QUASARS Eight single quasars have been detected from SDSS and found Object ID (objid), Right ascension (Ra) and Declination (Dec) as shown in table 1. Figures 1-8 show the absorption spectrum lines of the eight single quasars. Volume 3, Issue 5, May 014 Page 50
3 Table 1: Object ID, Right ascension, and Declination for Selected Single Quasars Quasar Name objid Ra Dec SDSS J SDSS J SDSS J SDSS J SDSS J SDSS J SDSS J SDSS J , Fig.1: Absorption Spectrum line of Quasar SDSS J Fig.: Absorption Spectrum line of Quasar SDSS J Fig3: Absorption Spectrum of Quasar SDSS J Volume 3, Issue 5, May 014 Page 51
4 Fig.4: Absorption Spectrum of Quasar SDSS J Fig.5: Absorption Spectrum of Quasar SDSS J Fig.6: Absorption Spectrum line of Quasar SDSS J Fig.7: Absorption Spectrum line of Quasar SDSS J Volume 3, Issue 5, May 014 Page 5
5 Fig8: Absorption Spectrum line of Quasar SDSS J We matching the wavelengths of the absorption lines in the spectrum λ obs ( ) of quasars at a value of flux F(λ), with those observed from the pure source in the laboratory λ rest () [7] Tables -9 reflects the extrapolated chemical elements for these single Quasars. By applying the equations which are mentioned previously, we found the features measured from absorption spectra as illustrated in Tables The relationship between the optical depths as a function of different values of redshift is shown in figure9. The linear relationship between Recession velocities as a function of distance is shown in figure 10. The slope determines the value of the Hubble constant. By drawing the relationship between the Look back times as a function of the redshift for different quasars as shown in figure 11, it clear that whenever the redshift is less whenever the value of look back time is higher. Table : The chemical composition of Quasar SDSS J Chemical Element F(λ) λ obs () λ rest () O II Ne II H Ɣ O III Table 3: The chemical composition of Quasar SDSS J Chemical Element F(λ) obs. rest C III Mg O II H Ɣ Ne II Table4: The chemical composition of Quasar SDSS J Chemical Elements F(λ) obs C IV He II C III Mg Table 5: The chemical composition of Quasar SDSS J Chemical Element F(λ) obs Lyα C IV C III Mg Volume 3, Issue 5, May 014 Page 53
6 Table 6: The chemical composition of Quasar SDSS J Chemical Element F(λ) obs rest Lyα C IV C III Table7: The chemical composition of Quasar SDSS J Chemical Element F(λ) obs Lyα C IV He II Table 8: The chemical composition of Quasar SDSS J Chemical Element F(λ) obs HeI Lyα S IV+OIV Table 9: The chemical composition of Quasar SDSS J Chemical Element F(λ) obs HeI N I Lyα Table10: The features measured of absorption line of quasar SDSS J Line V(Km/Sec) D(Mpc) M T(Gyr) n(h) X(H) Ʈ(GP) O II x x Ne II x x H Ɣ x x O III x x Average x x Table 11: The features measured of absorption line of Quasar SDSS J Line V (km/ sec) D(Mpc) M T(Gyr) n(h) (cm -3 ) X(H) Ʈ(GP) C III X X Mg X X O II X X H Ɣ X x X Ne II X X Average X X Volume 3, Issue 5, May 014 Page 54
7 Line Table 1: The features measured of absorption line of Quasar SDSS J V (Km/ Sec) D(Mpc) M T(Gyr) Table13: The features measured of absorption line of Quasar SDSS J n(h) (cm -3 ) X(H) Ʈ(GP) C IV X X He II X X C III X X Mg X X Average X X Line V D(Mpc) T(Gyr) n(h) (cm (Km/Sec) M X(H) ) Ʈ(GP) Lyα X X C IV X X C III X X Mg X X Average X X Table 14: The features measured of absorption line of Quasar SDSS J Line V(Km/Sec) D(Mpc) M T(Gyr) n(h) (Cm -3 ) X(H) Ʈ(GP) Lyα X X C IV X X C III X X Average X X Table 15: The features measured of absorption line of Quasar SDSS J Line V (Km/Sec) D(Mpc) M T(Gyr) n(h) (Cm -3 ) X(H) Ʈ(GP) Lyα X X C IV X X He II X X Average X X Table16: The features measured of absorption line of Quasar SDSS J Line V(Km/Sec) D(Mpc) M T(Gyr) n(h) (Cm -3 ) X(H) Ʈ(GP) He I X X Lyα X X S X X IV+OIV Average X X Volume 3, Issue 5, May 014 Page 55
8 Table 17: The features measured of absorption line of Quasar SDSS J Line V(Km/Sec) D(Mpc) M T(Gyr) n(h) (cm -3 ) X(H) Ʈ(GP) He I X X N I X X Lyα X X Average X X Fig9: Relationship between Optical depth and Redshift. Fig.10: Relationship between Velocity and Distance Fig.11: Relation between Look back time and Redshift 4. SPECTRAL ANALYSIS of DOUBLE QUASARS Four double quasars have been detected from SDSS and found Object ID (objid), Right ascension (Ra) and Declination (Dec) as shown in table 18. Figures 1-15 show the absorption spectrum lines of these quasars. Tables 19- reflect the extrapolated chemical elements for these quasars. The features measured from absorption spectra are illustrated in Tables 3-6. Also, we can find that the relationship between the optical depth as a function of different values of redshift of some simple of double quasars, as shown in figure 16. Figure 17 illustrates the linear relationship between recession velocities as a function of distance. By drawing the relationship between the Look back times as a function of the redshift of different quasars, we find that whenever the redshift is less whenever the value of look back time is higher (see figure 18). Table 18: Object ID, Right ascension, and Declination for Selected Double Quasars Quasar Name objid Ra Dec SDSS J , SDSS J , , SDSS J , , SDSS J , , Volume 3, Issue 5, May 014 Page 56
9 Fig. (1): Absorption Spectrum line of Quasar SDSS J Fig13: Absorption Spectrum line of Quasar SDSS J Fig.14: Absorption Spectrum line of Quasar SDSS J Fig.15: Absorption Spectrum line of Quasar SDSS J Volume 3, Issue 5, May 014 Page 57
10 Table (19): The chemical composition of Quasar SDSS J Chemical Element F(λ) obs C III C II Mg II Ne IV Ne V Table (0): The chemical composition of Quasar SDSSJ Chemical Element F(λ) obs C III Mg II Ne IV C II He I Table (1): The chemical composition of Quasar SDSSJ Chemical Element F(λ) obs Lyα N V O I C II C IV Table (): The chemical composition of Quasar SDSSJ Chemical Element F(λ) obs Lyα N V C IV C III O IV Table (3): The features measured of Quasar SDSS J Line V(Km/Sec) D(Mpc) M T(Gyr) n(h) (cm-3) X(H) Ʈ(GP) C III X X C II X X Mg II X X Ne IV X X Ne V X X Average X X Table (4): The features measured of Quasar SDSSJ n(h) (Cm- Line V(Km/Sec) D(Mpc) M T(Gyr) X(H) Ʈ(GP) 3) C III X X Mg II X X Volume 3, Issue 5, May 014 Page 58
11 Ne IV X X C II X X He I X X10 - Avera ge X X Table (5): The features measured of Quasar SDSS J n(h) (Cm- Line V(Km/Sec) D(Mpc) M T(Gyr) X(H) Ʈ(GP) 3) Lyα X X N V X X O I X X C II X X C IV X X Average X X Table (6): The features measured of Quasar SDSS J Line V(Km/Sec) D(Mpc) M T(Gyr) n(h) (Cm-3) X(H) Ʈ(GP) Lyα X X N V X X C IV X X C III X X O IV X X Average X X Fig.16: Relation between Optical depth and Redshift Fig.17: Relation between Velocity and Distance Volume 3, Issue 5, May 014 Page 59
12 Fig18: Relation between Lookback time and Redshift 5. CONCLUSIONS In this paper, the absorption spectra of eight single and four double quasars were studied and analyzed, We found that mostly elements of spectra single quasars are (O II, O III, Mg, H Ɣ, Ne II, C III, He II, and sometime He I, N I), but mostly elements of spectra double quasars are (C II, C III, Mg II, Ne IV, N V, and Sometimes O I, O IV, Ne V). From the results, it is found that the single quasars span a redshift range of z 6.47and the double quasars span a redshift of 1.01 z The features of absorption line, speed, distance, relativistic redshift, magnification, post-recombination density, look back time and Gunn-Peterson Optical depth were calculated. The value of magnification always less than one if speed of quasar is less than the speed of light (if v<c always M<1)..Also the results indicated that whenever the redshift is less whenever the value of look back time is higher and the value of optical depth is less. References [1] Allison. R. Hill, S. C. Gallagher, R. P. Deo, E. Peeters and Gordon. T. Richards," Characterizing Quasars in the Midinfrared: High Signal-to-Noise Spectral Templates", Mon. Not. R. Astron. Soc., 013. [] Valentina D., " Quaser Absorption Spectra: Probes Of The Baryonic Gas At High Redshift ", Ph.D. thesis submitted to Isis-international school for advanced studies,1999. [3] Gisella D. "A comprehensive analysis of optical and near-infrared spectroscopy of z_6 quasars",ph.d thesis submitted to Combined Faculties of the Natural Sciences and Mathematics,University of Heidelberg, Germany,011. [4] Huang, W.-R., Chen,.-F., Qin,Y.-P.,. Li, Liao M.-S, He, R.-H., Han W.-W., F., hong, Y.-Q., Gan J.-Q. and hou,w. "Identification of MgII Absorption Line Systems from SDSS Quasar Catalogue" J. Astrophys. Astr., 3, 77 80, 011. [5] Liddle, A., "An Introduction to Modern Cosmology second Edition ", West Sussex PO19 8SQ, 003. [6] "Quasar Absorption Lines" [7] Sloan Digital Sky Survey Authors Bushra Q. Al-Abudi received Ph.D. degree in Astronomy in 00 from University of Baghdad, College of Science, Department of Astronomy and Space. Currently she is professor in Astronomy department and her research interests include spectroscopy and photometry analysis of binary stars. Nuha S. Fouad received B.Sc. degrees in Astronomy in 01 from university of Baghdad, College of Science, Department of Astronomy and Space. Currently she is M.Sc. student in Astronomy department. Volume 3, Issue 5, May 014 Page 60
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