Fe Line Strength Research Articles

The XMM deep survey in the CDFS

We present the X-ray spectra of 185 bright sources detected in the XMM-Newton deep survey of the Chandra Deep Field South with the three EPIC cameras combined. The 2–10 keV flux limit of the sample is 2 × 10−15 erg s−1 cm−2. The sources are distributed over a redshift range of z = 0.1−3.8, with 11 new X-ray redshift measurements included. A spectral analysis was performed using a simple model to obtain absorbing column densities, rest-frame 2–10 keV luminosities, and Fe K line properties of 180 sources at z > 0.4. Obscured AGN are found to be more abundant toward higher redshifts. Using the XMM-Newton data alone, seven Compton-thick AGN candidates were identified, which set the Compton-thick AGN fraction at ≃4%. An exploratory spectral inspection method with two rest-frame X-ray colours and an Fe line strength indicator was introduced and tested against the results from spectral fitting. This method works reasonably well to characterise a spectral shape and can be useful for a pre-selection of Compton-thick AGN candidates. We found six objects exhibiting broad Fe K lines out of 21 unobscured AGN of best data quality, implying a detection rate of ∼30%. Five redshift spikes, each with more than six sources, are identified in the redshift distribution of the X-ray sources. Contrary to the overall trend, the sources at the two higher redshift spikes, at z = 1.61 and z = 2.57, exhibit a puzzlingly low obscuration.

Kinematics and line strength indices in the halos of the Coma brightest cluster galaxies NGC 4874 and NGC 4889

We investigate the stellar kinematics and line strength indices in the outer halos of brightest cluster galaxies (BCGs) in the Coma cluster to obtain the outer halo V_rot and sigma profiles and to derive constraints on the formation history of these objects. Methods: We analyzed absorption lines in deep, medium-resolution, long-slit spectra in the wavelength range ~ 4500 - 5900 Angstrom, out to ~50 kpc for NGC 4874 and ~65 kpc for NGC 4889, probing regions with a surface brightness down to mu_R ~24 mag/arcsec^2. Results: These data provide stellar velocity and velocity dispersion profiles along the major axes of both BCGs, and also along the minor axis of NGC 4889. The kinematic properties of NGC 4874 and NGC 4889 halos extend the previous relations of early-type galaxy halos to bright luminosities and indicate that the stars in the outer regions are still bound to these galaxies. For NGC 4889 we also determine Hbeta, Mg and Fe line strength indices, finding strong radial gradients for Mg and Fe. The current dataset for NGC 4889 is one of the most extended in radius, including both stellar kinematics AND line strength index measurements.

THE DISTRIBUTION AND COSMIC DENSITY OF RELATIVISTIC IRON LINES IN ACTIVE GALACTIC NUCLEI

X-ray observations of several active galactic nuclei show prominent iron K-shell fluorescence lines that are sculpted due to special and general relativistic effects. These observations are important because they probe the space-time geometry close to distant black holes. However, the intrinsic distribution of Fe line strengths in the cosmos has never been determined. This uncertainty has contributed to the controversy surrounding the relativistic interpretation of the emission feature. Now, by making use of the latest multi-wavelength data, we show theoretical predictions of the cosmic density of relativistic Fe lines as a function of their equivalent width and line flux. We are able to show unequivocally that the most common relativistic iron lines in the universe will be produced by neutral iron fluorescence in Seyfert galaxies and have equivalent widths < 100 eV. Thus, the handful of very intense lines that have been discovered are just the bright end of a distribution of line strengths. In addition to validating the current observations, the predicted distributions can be used for planning future surveys of relativistic Fe lines. Finally, the predicted sky density of equivalent widths indicate that the X-ray source in AGNs can not, on average, lie on the axis of the black hole.

Spatially Resolved Spectroscopy of Coma Cluster Early‐Type Galaxies. IV. Completing the Data Set

The long-slit spectra obtained along the minor axis, offset major axis, and diagonal axis are presented for 12 E and S0 galaxies of the Coma Cluster drawn from a magnitude-limited sample studied before. The rotation curves, velocity dispersion profiles, and the H3 and H4 coefficients of the Hermite decomposition of the line-of-sight velocity distribution are derived. The radial profiles of the Hβ, Mg, and Fe line strength indices are measured too. In addition, the surface photometry of the central regions of a subsample of four galaxies recently obtained with the Hubble Space Telescope is presented. The data will be used to construct dynamical models of the galaxies and study their stellar populations.

Stellar abundance gradients in galactic discs - I. Method and spectral line gradients

We describe the technique of absorption-line imaging of galaxy discs using the Taurus Tunable Filter on the Anglo-Australian Telescope and demonstrate its sensitivity to the behaviour of spectral features associated with Mg and Fe. Radial profiles of Mg 2 and Fe5270 line strengths are presented for a sample of eight face-on spiral galaxies spanning a range of Hubble types. Signatures of phenomena including merger-induced star formation, H II rings and galactic bars are also reported. This study demonstrates the capacity of tunable filters to measure Mg and Fe line strengths across the face of spiral galaxies, which can ultimately reveal clues about the star formation history and chemical evolution.

Kinematic Profiles of SO Galaxies

view Abstract Citations (113) References (65) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Kinematic Profiles of SO Galaxies Fisher, David Abstract Stellar rotation curves, velocity dispersion profiles, and line-of-sight velocity distributions (LOSVD) as derived from absorption lines are presented for the major axes of 18 S0 and two elliptical galaxies. Ionized gas rotation curves and dispersions were measured from the [0 III] 5007 Å emission line in the 9 S0 galaxies displaying this feature. Minor-axis results are given for 14 of the S0 galaxies and one of the ellipticals. A wide range of behaviors are observed in the rotation and velocity dispersion profiles. These variations could be the result of the superposition of stars and gas belonging to the disks and bulges as well as the possible influences of bars, nuclear disks, and warps. Deviations from a Gaussian LOSVD are found along the major axes of all the galaxies in our sample. As parametrized by the Gauss-Hermite series of orthogonal functions, asymmetric deviations are always found in the inner regions of the S0 galaxies such that the prograde wing of the LOSVD is steeper than the retrograde wing. This is similar to the behavior observed in elliptical galaxies. However, at larger radii these asymmetries can change their sign. We find that in 9 of the 18 S0 galaxies a high-speed tail to the LOSVD develops along the major axis beyond the central regions. In 3 of these 9 objects the LOSVD asymmetries display a second change of sign with radius such that a low-speed tail is again present and persists to our last measured values. No correlations were found between the sizes of the stellar velocity dispersion gradients and either central velocity dispersion, absolute magnitude, disk-to-bulge ratio, Mg2 or Fe line strength gradients. For the objects in our sample with edge-on orientations a comparison between the minor-axis `bulge' velocity dispersion gradients and those found in elliptical galaxies indicates that the S0 bulges display, on average, logarithmic gradients approximately 4 times steeper than those found in normal luminous ellipticals. A number of galaxies show particularly interesting features. For the LINER S0 galaxy NGC 3998 we find that the velocity dispersion profiles of both the stars and gas rise sharply towards the center reaching nuclear values of o=320 km s '. Nuclear disks of rapidly rotating gas are found in NGC 4350 and NGC 4762. A nuclear stellar disk is apparent in the edge-on galaxy NGC 4111 and an extended disk of counterrotating gas is observed in the barred S0 NGC 3941. Publication: The Astronomical Journal Pub Date: March 1997 DOI: 10.1086/118312 Bibcode: 1997AJ....113..950F full text sources ADS | data products SIMBAD (20) NED (20) CDS (1)

Line Strengths and Line-Strength Gradients in S0 Galaxies

view Abstract Citations (150) References (100) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Line Strengths and Line-Strength Gradients in S0 Galaxies Fisher, David ; Franx, Marijn ; Illingworth, Garth Abstract Line strengths and their gradients in Mg, Fe, and Hβ have been determined for a sample of 20 S0 galaxies in order to study the stellar populations of their bulges and disks and to investigate their relationship to elliptical galaxies. Data are also presented for the elliptical galaxy NGC 1700 and the E/S0 NGC 3585. We find that S0 galaxies generally follow a similar, though possibly steeper, relationship between central Mg_2_ line strength and central velocity dispersion as found for elliptical galaxies. The S0 galaxies show no dependence between Fe line strengths and central velocity dispersion similar to the behavior observed in elliptical galaxies. The central Mg/Fe ratios in the luminous S0 galaxies show an overabundance of Mg to Fe with respect to solar element ratios. The disks (at 1 h) and bulges (at 1 r_e_) show Mg/Fe ratios lower than those found in the central regions. The magnitudes of the Mg and Fe line-strength gradients within the galaxies are found to be correlated, i.e., objects with steep Mg gradients have correspondingly large Fe gradients. We infer bulge and disk gradients for the nine most edge-on galaxies for which we have both major and minor-axis profiles. The metal line strengths decrease with radius along the major and minor axes in the bulge-dominated central regions. At larger radii, however, the major-axis metal line strength profiles flatten while the minor-axis bulge profiles fall to lower values. Representative color maps in B - R are presented that display a separation between bulge and disk colors corresponding to the metal line strength profiles. Based on our Mg_2_ profiles, the average metal gradient found in the disks of our sub-sample is {DELTA}[Fe/H]/{DELTA}(r/h) = -0.08 +/- 0.06, which corresponds to a reduction in the mean metallicity of the disk stellar population by <~ 15% per disk scale length (h). These shallow metallicity gradients are approximately a factor of 2-3 smaller than those derived for the disks of late-type spiral galaxies from H II regions and are consistent with previous investigations that showed a trend for disk metallicity gradients to decrease toward earlier Hubble types. As inferred from our Mg and Fe line strengths, the mean size of the bulge metallicity gradients is {DELTA}[Fe/H]/{DELTA}log r = - 0.7 +/- 0.4 which is steeper than typical elliptical galaxy gradients. Our findings do not support formation scenarios in which bulges formed either from heated disk material at late times after disk formation or through dissipationless stellar merging, as neither process includes mechanisms for producing the observed metallicity gradients. Our observations are better explained in terms of formation via dissipative collapse (or merging) at early times. Publication: The Astrophysical Journal Pub Date: March 1996 DOI: 10.1086/176873 Bibcode: 1996ApJ...459..110F Keywords: GALAXIES: ABUNDANCES; GALAXIES: ELLIPTICAL AND LENTICULAR; CD; GALAXIES: STELLAR CONTENT full text sources ADS | data products NED (26) SIMBAD (22) CDS (1)

Optical Spectroscopy of the Red Horizontal Branch Stars of NGC 6791

view Abstract Citations (13) References (35) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Optical Spectroscopy of the Red Horizontal Branch Stars of NGC 6791 Hufnagel, Beth ; Smith, Graeme H. ; Janes, Kenneth A. Abstract We have obtained 3600-4600 Å spectra at ∼5 Å resolution for 31 stars in the field of NGC 6791, one of the oldest and most "globular-cluster-like" of the Galactic open clusters. Based on spectroscopic analysis of 19 of these stars considered to be red horizontal branch (RHB) members of NGC 6791, we conclude that there is no evidence for significant variations in the CR band or the Ca and Fe line strengths among these stars, although there are strong indications of intrinsic differences among the CN band strengths. There is also no evidence for correlations between the CN band, CR band, or Fe line strengths of these stars, although there may be a weak correlation between CN band and Ca line strengths. The nature of the CN-band inhomogeneity is in marked contrast to the bimodal CN distributions discovered among the RHB stars of the two globular clusters 47 Tuc and M71 by Norris & Freeman [ApJ, 254, 143 (1982)] and Smith & Penny [M, 97, 1397 (1989)]. These results imply that either the environment within which globular clusters formed resulted in initial C and N abundance inhomogeneities that were lacking in NGC 6791, or that the evolutional processes which alter stellar surface abundances prior to or during the core helium-burning phase of evolution, differ in some respect between the disk globular clusters and NGC 6791. Publication: The Astronomical Journal Pub Date: August 1995 DOI: 10.1086/117554 Bibcode: 1995AJ....110..693H Keywords: GLOBULAR CLUSTERS: INDIVIDUAL: NGC 6791; STARS: ABUNDANCES full text sources ADS | data products SIMBAD (41)

Line-strengths in early-type galaxies

Summary We have analysed Mg, H/β and Fe line-strengths in a sample of elliptical, SO and brightest cluster galaxies. For 15 galaxies, our spectra extend to approximately the half-light radius (re), and we are able to measure radial line-strength gradients. The metallic line-strength gradients vary markedly from object to object, and do not correlate strongly with parameters such as total luminosity and rotation, though we find some evidence that gradients in the Mg2 index correlate with central velocity dispersion and central line-strength. The highly variable line-strength gradients in early-type galaxies shows that they have experienced different star formation histories. We suggest that this may be explained if they formed by the mergers of subunits in which star formation had proceeded to varying degrees of completion. We find that the line-strengths at r ˜ re in elliptical galaxies are slightly larger than those of metal-rich galactic globulars, suggesting that typical elliptical galaxies have roughly solar abundance at r~re and therefore that most ellipticals have relatively weak abundance gradients. The relative line-strengths in the outer parts of ellipticals differ from those in the nuclei of low-luminosity ellipticals, indicating that these stellar populations do not represent a simple one-parameter family governed by mean metal abundance. We find no significant differences in the central Mg and Fe line-strengths of the brightest cluster galaxies and normal ellipticals with the same central velocity dispersion. However, we find that two cD galaxies show H/β in emission and are also at the centres of the prodigious cooling flows with mass-deposition rates of ≳ 100 M⊙ yr−1. Galaxies with cooling flows have identical Mg and Fe line-strengths to galaxies without cooling flows. We show that this implies that only a small fraction of the total luminosity of cooling flow galaxies could come from ongoing star formation with a normal stellar initial mass function.

N-TYPE CARBON STARS AND THE 3-ALPHA PROCESS.

ABSTRACT High-dispersion yellow-red spectra of eight representative N-type carbon stars have been matched by Minneart model synthesis. CN, C2, and Fe line strengths imply high abundances of free carbon, C- 0, such that N-star surface carbon must originate from 3-o He- shell burning, rather than from CNO equilibrium processes. CN/C2 ratios ranging from 4 to 200 imply values of log (C - 0)/H from -2.7 to -4.5; these lead to ClO ratios from 2.9 to 1.033, if the oxygen abundances are solar. Nitrogen abundances for these stars are also essentially solar, with a mean value log (N/H) = - 4.10 0.18, also ruling out substantial contributions from C NO processing. Values of the '2C/'3C ratio range from 3.5 to > 25. Zr/Ti ratios are a factor of 2 to 10 greater than solar, similar to the S stars. Ba is enriched only in some high Zr stars. Rareearth abundances are subject to severe error. Lithium abundances range from the meteoritic to below solar. The range of log g is -0.3 to 1.7. Excitation temperatures, both atomic and and molecular, are between 2500 K and 3150 K. Microturbulent velocities are in most cases near 6 km sec-1. Relations to other red-giant stars are considered. Key words: carbon stars - abundances - nucleosynthesis