Luminosity - Spectral Index Dependence of X-ray Bright Seyfert Galaxies

TL;DR

This study analyzes X-ray luminosities and spectral indices of 97 Seyfert 1 galaxies, suggesting a complex emission model and proposing a relation between black hole mass, merging stage, and X-ray properties.

Contribution

It introduces a two-parametric emission model and links black hole mass and merging stage to X-ray spectral features in Seyfert galaxies.

Findings

Distribution of luminosities and spectral indices appears random.

A two-parametric emission model is necessary.

Proposed relation between black hole mass, merging stage, and X-ray parameters.

Abstract

X-ray luminosities and spectral indices of 97 bright Seyfert 1 galaxies from XMM archive are analyzed in this article. Distribution of these values is random so we conclude that the model of emission should be at least two-parametric. Within the merging model of AGN the relation between black hole mass, stage of merging and observable X-ray parameters is proposed.

Tables

Table 1. Table 1: General parameters of new Seyfert 1 galaxies added to analysis. The rest sample see in [ 17 ] . u - u-band apparent magnitude; r - major semiaxis of 25 / ′′ m {}^{m}/^{\prime\prime} contour; V K 3 subscript 𝐾 3 {}_{3}K - radial velocity in CMB reference frame. Parameters were taken from Hyperleda database.

N	Name	RA, deg	DEC, deg	Coord. num.	u	r, arcsec	V3K, km/s
1	2MASX J00044124+0007113	1,1718	0,1198	0004+0007	18,63	6,3	31923
2	ESO 540-1	8,5571	-21,4389	0034-2126	13,71	37,8	7744
3	2MASX J00440466+0101531	11,0195	1.0313	0044+0101	17,77	9,3	33210
4	2MASX J00565517-7513524	14,2297	-75,2312	0056-7513	15,04	6,4	22137
5	Mrk 993	21,3812	32,1360	0125+3208	14,37	47,6	4380
6	3C 59	31,7590	29,5128	0207+2930	17,44	11,1	32612
7	UGC 1841	35,7989	42,9914	0223+4259	13,75	65,7	6167
8	2MASX J02491286-0815254	42,3036	-8,2571	0249-0815	16,64	14,0	8617
9	ESO 359-19	61,2570	-37,1876	0405-3711	15,52	17,3	16476
10	3C 111	64,5885	38,0266	0418+3801	19,75	10,0	15305
11	Mrk 1506	68,2962	5,3542	0433+0521	15,06	23,3	9839
12	ESO 15-11	68,8183	-78,0323	0435-7801	15,58	20,3	18351
13	RBS 560	69,3672	-47,1916	0437-4711	16,61	7,4	15574
14	UGC 3142	70,9449	28,9718	0443+2858	15,84	28,0	6434
15	Pictor A	79,9570	-45,7789	0519-4546	16,25	14,7	10516
16	IRAS 05218-1212	81,0288	-12,1693	0524-1210	15,70	7,6	14721
17	2E 1644	95,7820	-64,6060	0623-6436	17,06	15,0	36197
18	2MASX J07185777+7059209	109,7410	70,9891	0719+7059	17,40	5,9	19810
19	2E 1891	119,5000	39,3414	0754+3928	15,21	2,0	28935
20	Sextans Ring	150,5010	-8,1614	0959-0809	15,22	13,0	4910
21	MCG +11-19-030	239,2650	63,8408	1557+6350	15,42	20,8	9000
22	2MASX J16115141-6037549	242,9640	-60,6319	1611-6037	14,70	26,7	4777
23	2MASX J16174561+0603530	244,4400	6,0649	1617+0603	16,19	14,4	11479
24	Mrk 883	247,4700	24,4439	1629+2426	15,78	18,1	11447
25	2E 4097	278,7640	32,6964	1835+3241	15,15	21,2	17289
26	FRL 339	302,9930	-57,0868	2011-5705	16,12	14,4	16274
27	4C 74.26	310,6560	75,1341	2042+7508	15,33	2,0	31071
28	Mrk 509	311,0410	-10,7235	2044-1043	13,35	17,7	10045
29	2MASX J21022164+1058159	315,5900	10.9711	2102+1058	14,92	12,6	8336
30	2MASX J22191855+1207531	334,8270	12.1315	2219+1207	17,19	8,3	24229
31	3C 445	335,9570	-2,1036	2223-0206	17,26	8,9	16510
32	NGC 7469	345,8150	8,8739	2303+0852	12,90	41,4	4545
33	NGC 7589	349,5650	0,2612	2318+0015	15,23	28,7	8578
34	NGC 7603	349,7360	0,2440	2318+0014	14,04	36,1	8484
35	NGC 7720	354,6230	27,0317	2338+2701	13,43	45,4	8695
36	MCG -05-01-013	359,3665	-30,4613	2357-3027	14,96	16,9	8744

Table 2. Table 2: X-ray parameters of Seyfert 1 galaxies. F X subscript 𝐹 𝑋 F_{X} - X-ray flux in 2-10 keV band in 10 − 14 ​ e ​ r ​ g / s / c ​ m − 2 superscript 10 14 𝑒 𝑟 𝑔 𝑠 𝑐 superscript 𝑚 2 10^{-14}erg/s/cm^{-2} ; L X ​ 40 subscript 𝐿 𝑋 40 L_{X40} - X-ray luminosity in redshift space for H=70 km/s/Mpc divided by 10 40 superscript 10 40 10^{40} erg/s; Γ Γ \Gamma - spectral index; N H subscript 𝑁 𝐻 N_{H} - neutral hydrogen column density; for the spectra fitted in this work χ 2 / d ​ o ​ f superscript 𝜒 2 𝑑 𝑜 𝑓 \chi^{2}/dof is presented instead of reference.

N	Target	$F_X$	$\Delta F_X$	$L_{X40}$	$\Gamma$	$\Delta \Gamma$	$N_H,{10}^{20}c{m}^{-2}$	Ref	$lg\left(M_{BH}/M_{\odot }\right)$
1	0004+0007	45,6	1,9	1080	1,840	0,098	0,013$\pm$0,011	28,46/29	7,873 $\pm$0,233
2	0034-2126	80,1	2,2	112	1,440	0,100		[6]	6,489 $\pm$0,235
3	0044+0101	110,5	8,7	2831	1,806	0,174	0,063$\pm$0,027	74,98/34	8,258 $\pm$0,309
4	0056-7513	557,0	14,6	6339	2,118	0,056	0,046$\pm$0,008	113,13/61	8,920 $\pm$0,191
5	0125+3208	216,6	3,4	96	1,710	0,060	0,07$\pm$0,01	[4]	6,694 $\pm$0,195
6	0207+2930	1434,4	4,5	35428	1,398	0,006	0,0013$\pm$0,0007	4765,6/998	8,947 $\pm$0,141
7	0223+4259	50,4	1,4	45	0,870	0,200		[5]	5,518 $\pm$0,335
8	0249-0815	65,3	4,2	113	2,041	0,151	0,013$\pm$0,015	18,07/23	7,094 $\pm$0,286
9	0405-3711	612,4	7,9	3861	1,764	0,019	0$\pm$0,006	28,12/17	8,351 $\pm$0,154
10	0418+3801	8202,2	17,5	44619	1,700	0,020	0,8	[10]	9,349 $\pm$0,155
11	0433+0521	8159,1	16,0	18343	1,860	0,010	0,01$\pm$0,001	[1]	9,122 $\pm$0,145
12	0435-7801	251,9	4,2	1970	1,894	0,050	0.051$\pm$0,008	78,48/65	8,188 $\pm$0,185
13	0437-4711	1203,9	5,6	6781	2,247	0,097	0$\pm$0,001	598,7/248	9,078 $\pm$0,232
14	0443+2858	2179,5	16,2	2095	0,985	0,029	1,217$\pm$0,045	498.34/211	7,307 $\pm$0,164
15	0519-4546	1784,9	4,7	4584	1,800	0,010	0,03$\pm$0,01	[20]	8,461 $\pm$0,145
16	0524-1210	454,4	8,6	2287	9,500	9,900	0,909$\pm$0,464	143,54/28	-
17	0623-6436	818,0	8,4	24890	2,034	0,025	0,021$\pm$0,003	246,18/213	9,430 $\pm$0,160
18	0719+7059	147,5	12,3	1344	1,971	0,235	0,024$\pm$0,045	2,15/5	8,098 $\pm$0,490
19	0754+3928	382,1	5,0	7429	7,372	0,621	0,234$\pm$0,043	396,04/40	-
20	0959-0809	1078,5	6,7	604	2,432	0,023	0,066$\pm$0,002	783.18/540	8,213 $\pm$0,158
21	1557+6350	50,7	6,0	95	2,082	0,206	0$\pm$0,072	5,77/5	7,061 $\pm$0,476
22	1611-6037	907,8	27,7	481	1,712	0,059	0,131$\pm$0,016	67,21/56	7,394 $\pm$0,194
23	1617+0603	1596,9	14,6	4887	1,957	0,017	0,021$\pm$0,002	535,78/495	8,646 $\pm$0,152
24	1629+2426	287,9	4,2	876	1,689	0,054	0,103$\pm$0,014	53,73/57	7,632 $\pm$0,189
25	1835+3241	6930,5	24,1	48110	2,150	0,180	3$\pm$1	[13]	9,832 $\pm$0,315
26	2011-5705	296,9	3,8	1826	2,576	0,062	0,039$\pm$0,006	94,80/67	8,838 $\pm$0,197
27	2042+7508	3857,2	10,0	86479	1,860	0,010	0,183	[2]	9,797 $\pm$0,145
28	2044-1043	8290,5	10,2	19427	1,970	0,010	0,27$\pm$0,01	[20]	9,258 $\pm$0,145
29	2102+1058	154,8	17,6	250	1,736	0,108	0,131$\pm$0,025	28,12/17	7,134 $\pm$0,376
30	2219+1207	466,2	4,1	6356	3,099	0,019	0,074$\pm$0,002	523,61/233	9,902 $\pm$0,154
31	2223-0206	875,2	12,0	5540	1,4	0,1	1 - 10	[11]	8,143 $\pm$0,235
32	2303+0852	5311,5	14,5	2548	1,980	0,010	45$\pm$2	[20]	8,387 $\pm$0,145
33	2318+0015	71,2	2,7	122	1,768	0,093	0,036$\pm$0,021	11,84/21	6,854 $\pm$0,228
34	2318+0014	4597,2	32,9	7685	2,280	0,030	14,8$\pm$5,6	[12]	9,165 $\pm$0,165
35	2338+2701	62,9	12,1	110	2	0,5	0,5$\pm$0,2	[7]	7,041 $\pm$0,905
36	2357-3027	1060,8	46,5	1884	2,455	0,028	0,096$\pm$0.002	401,5/302	8,729 $\pm$0,163

Table 3. Table 3: Distribution of black hole mass in units of σ 𝜎 \sigma .

Interval	<-3	(-3,-2)	(-2,-1)	(-1,0)	(0,1)	(1,2)	(2,3)	>3
Number of galaxies	1	2	14	28	37	15	0	0
%	1,0	2,1	14,4	28,9	38,1	15,5	0	0
Number of galaxies in [21]	1	0	1	12	13	5	0	0
%	3,1	0	3,1	37,5	40,6	15,6	0	0
Normal distribution, %	0,2	2,1	15,6	32,1	32,1	15,6	2,1	0,2

Equations

$$\Gamma =lg(t/10^{6}years).$$

$$lg(M_{BH}/M_{\odot })=lg{L}_X+\Gamma -A,$$

$$lg(M_{BH}/M_{\odot })=7.992\pm \mathrm{0.562.}$$

Full text

Key words: X-rays: galaxies, galaxies: Seyfert

Taras Shevchenko National University of Kyiv, Glushkova ave., 4, 03127, Kyiv, Ukraine

tugay@anatoliy@gmail.com

Introduction

XMM-Newton observations archive is the largest and the most convenient database for the analysis of X-ray spectra of any celestial bodies including extragalactic. Xgal sample of X-ray galaxies ([15], [19]) contains more than 4000 XMM sources associated with galaxies or galaxy clusters. The main goal of compiling Xgal was the study of a large-scale structure (LSS) of the Universe in X-ray band (0.2-15 keV for XMM). The distribution of the main elements of LSS - filaments, voids and walls - can be recovered for redshifts up to 0.2 ([16], [18]). It was shown in [14] and [17] that the most frequent type of X-ray emitting galaxies at such distances is Seyfert 1. Spectra of Seyfert 1 galaxies in SDSS region were analyzed in [17]. 30 of them are Compton thin ($N_{H}<10^{25}cm^{-2}$) and thus can be correctly fitted by the powerlaw. The rest bright Sy 1 X-ray galaxies with radial velocities from 4000 to 39000 km/s are studied in present work. We compiled a list of major X-ray galaxies in nearby Universe - Compton thin Sy 1 galaxies. Our goal was to calculate spectral parameters of these galaxies, to build the distribution of that parameters and to choose some realistic connection between observed spectral parameters and the parameters of internal structure of AGN.

Sample selection and X-ray spectral analysis

The statistics of galaxies considered for this work is the following. There are 582 bright X-ray extragalactic sources outside SDSS region. 87 of them are Seyfert 1. The resulting list of bright Sy 1 galaxies from Xgal sample consists of three parts:

1. Spectral parameters for 30 Sy 1 galaxies in SDSS region were obtained previously in [17].

2. 23 new spectra were built in the present work using the standard XMM SAS package. We get event lists for PN camera with epproc procedure, filtered them from solar protons with parameters 150<PI<15000 and PATTERN=0 and derived spectra with especget procedure. Background region was selected from the same CCD chip as the source and of the same size.

3. 46 spectra were found from literature. 33 of them were from CAIXA - Catalog of AGNs in XMM Archive ([3]).

Parameters of Sy 1 galaxies from p.2 and p.3, except for CAIXA entries, are presented in Tables 1 and 2. The main observable parameters of X-ray emission are luminosity and a spectral index. In most cases of compton thin Sy 1 galaxies these are the only X-ray emission parameters that can be fitted correctly. The distribution of these parameters is presented at Fig. 1. Another important spectral feature in 2-15 keV energy band is the iron emission line at 6.5 keV, but it is detected rarely, so we do not consider it here. Also we find two galaxies with thermal dominated emission: 2E1891 and IRAS05218-1212. We found the best fit blackbody temperature $1.11\pm 0.03$ keV and $2.37\pm 0.13$ keV for these galaxies respectively. The powerlaw component was not fitted correctly for these galaxies so they were excluded from further analysis.

Interpretation of X-ray luminosity and spectral index

Previously analyzed parameters should be connected with some intrinsic parameters of AGN. In the model of Hopkins et al. (2008, [8]) AGN appears as a result of merging of two galaxies. Different observable features of AGN can be interpreted as stages of merging. According to this model it was supposed the simplest relation that the photon index equals to a decimal logarithm of time since collision:

[TABLE]

It was assumed here that at large times after merging hard X-ray emission decreases that could appear as the increasing spectral index. Since the central engine of AGN is assumed to be a supermassive black hole in its center, luminosity of AGN should correlate with the black hole mass. Taking into account the decreasing luminosity with the age, the following formula for estimating of the black hole mass is proposed:

[TABLE]

where $L_{X}$ is measured in erg/s. The physical reason of (2) is the assumption that the total amount of the emitted energy ($L_{X}\cdot t$) should be related to the total energy budget of the source (mass of the available gas, which might be proportional to $M_{BH}$). This relation has not yet been verified and may have unclear systematical uncertainty behind. Coefficient A=37.375 was selected to equalize the average black hole mass with the results of a similar work of Vestergaard and Peterson (2006, [21], hereafter VP), where the black hole masses for AGNs were also estimated from X-ray emission. The averaged logarithm of the black hole mass in [21] and for our sample equals (at 1$\sigma$ level)

[TABLE]

Two lines corresponding to the black hole mass of $10^{7}M_{\odot}$ and $10^{9}M_{\odot}$ are shown at Fig. 1. Masses of the central black holes of individual galaxies are presented in the last column of Table 2. The uncertainty of $lg(M_{BH}/M_{\odot})$ depends of the uncertainties of $\Gamma$, $L_{X}$ and systematic effects. According to (3), this uncertainty should be approximately equal to 0.5 or less. Black hole mass distributions for our sample and VP galaxies were approximated by Gaussian. Deviation for Xgal Sy1 galaxies appears somewhat larger than in [21] - $\sigma=0.826$. This value is potentially biased, as here we study solely the X-ray bright objects, whereas the VP sample, based on optical data, include both X-ray bright and dim sources. The distributions of the black hole masses for our sample and VP results are presented in Table 3. The percentage of normal Gaussian distribution is also given for the comparison. Width of bin is equal to 1 $\sigma$.

Conclusion and discussion

Distribution of X-ray emission parameters at Fig. 1 is random so we conclude that the model of galaxy emission should be at least two-parametric. We propose to consider the black hole mass and the merging stage as such intrinsic model parameters. Dependence of X-ray spectral index from X-ray luminosity was recently found in [22]. The authors considered the dependence of $\Gamma$ from $L_{X}/L_{Edd}$ ratio and interpreted this dependence by two-phase advection dominated accretion. In such study $L_{Edd}$ and black hole mass should be estimated independent from luminosity (for the method of $M_{BH}$ estimation by AGN X-ray emission see, for example, [9] ). It is possible in the case if the data of X-ray variability is available and the same source can show different values of $\Gamma$ and $L_{X}/L_{Edd}$ in the series of observations. The most Xgal object has only one XMM observation and all X-ray lightcurves for our Seyfert 1 galaxies are constant. So we can not consider $\Gamma(L_{X}/L_{Edd})$ dependence and conclude here the parameter no significant dependence of $\Gamma$ from $L_{X}$.

Acknowledgement

This work was performed at VIRGO.UA. The authors are thankful to ISDC High-Energy Astrophysics data centre for developing Ukrainian Virtual Roentgen and Gamma Observatory. A.Tugay thanks to anonymous referee for useful comments.