arXiv subjects

D. Ilic

Publications and source records attributed to D. Ilic.

32 records · Page 2Linked to original sources

arXiv2011

Observatons of NGC 3077 Galaxy in Narrow Band [SII] and H_alpha Filters

We present observations of the HI tidal arm near dwarf galaxy NGC 3077 (member of the M81 galaxy group) in narrow band [SII] and H_alpha filters. Observations were carried out in March 2011 with the 2m RCC telescope at NAO Rozhen, Bulgaria. Our search for possible supernova remnant candidates (identified as sources with enhanced [SII] emission relative to their H_alpha emission) in this region yielded no sources of this kind. Nevertheless, we found a number of objects with significant H_alpha emission that probably represent uncatalogued, low brightness HII regions.

astro-ph.CO↗

arXiv2011

Spectral optical monitoring of 3C 390.3 in 1995-2007: II. Variability of the spectral line parameters

A study of the variability of the broad emission-line parameters of 3C390.3, an active galaxy with the double-peaked emission-line profiles, is presented. We give a detail analysis of variation in the broad Ha and Hb profiles, the ratios, and the Balmer decrement of different line segments. Studying the variability of the line profiles we explore the disk structure, that is assumed to emit the broad double-peaked Ha and Hb emission lines. We divided the observed spectra in two periods (before and after the outburst in 2002) and analyzed separately the variation in these two periods. First we analyzed the spectral emission-line profiles of Ha and Hb, measuring the peak positions. Then, we divided lines into several segments, and we measured the line-segment fluxes. The Balmer decrement variation for total Ha and Hb fluxes, as well as for the line segments has been investigated and discussed. We modeled the line parameters variation using an accretion disk model. We compared the variability in the observed line parameters with the disk model predictions and found that the variation in line profiles and in line segments corresponds to the emission of a disk-like BLR. But, also there is probably one additional emission component that contributes to the Ha and Hb line center. We found that the variation in the line profiles is caused by the variation in the parameters of the disk-like BLR, first of all in the inner (outer) radius which can well explain the line parameter variations in the Period I. The Balmer decrement across the line profile has a bell-like shape, and it is affected not only by physical processes in the disk, but also by different emitting disk dimension of the Ha and Hb line. The geometry of the BLR of 3C390.3 seems to be very complex, and inflows/outflows might be present, but it is evident that the broad line region with disk-like geometry has dominant emission.

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arXiv2009

Optical Observations of M81 Galaxy Group in Narrow Band [SII] and H_alpha Filters: Holmberg IX

We present observations of the nearby tidal dwarf galaxy Holmberg IX in M81 galaxy group in narrow band [SII] and H$α$ filters, carried out in March and November 2008 with the 2m RCC telescope at NAO Rozhen, Bulgaria. Our search for resident supernova remnants (identified as sources with enhanced [SII] emission relative to their H$α$ emission) in this galaxy yielded no sources of this kind, besides M&H 10-11 or HoIX X-1. Nevertheless, we found a number of objects with significant H$α$ emission that probably represent uncatalogued HII regions.

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arXiv2009

Long-term variability of the optical spectra of NGC 4151: II. Evolution of the broad Ha and Hb emission-line profiles

Results of the long-term (11 years, from 1996 to 2006) H$α$ and H$β$ line variations of the active galactic nucleus of NGC 4151 are presented. High quality spectra (S/N>50 and R~8A) of H$α$ and H$β$ were investigated. We analyzed line profile variations during monitoring period. Comparing the line profiles of H$α$ and H$β$, we studied different details (bumps, absorption features) in the line profiles. The variations of the different H$α$ and H$β$ line profile segments have been investigated. Also, we analyzed the Balmer decrement for whole line and for line segments. We found that the line profiles were strongly changing during the monitoring period, showing blue and red asymmetries. This indicates a complex BLR geometry of NGC 4151 with, at least, three kinematically distinct regions: one that contributes to the blue line wing, one to the line core and one to the red line wing. Such variation can be caused by an accelerating outflow starting very close to the black hole, where the red part may come from the region {closer to the black hole than the blue part, which is coming} from the region having the highest outflow velocities. Taking into account the fact that the BLR of NGC 4151 has a complex geometry (probably affected by an outflow) and that a portion of the broad line emission seems to have not a pure photoionization origin, one can ask the question whether the study of the BLR by reverberation mapping may be valid in the case of this galaxy.

astro-ph.GA↗

arXiv2009

Long term variability of the Broad Emission Line profiles in AGN

Results of a long-term monitoring ($\gtrsim 10$ years) of the broad line and continuum fluxes of three Active Galactic Nuclei (AGN), 3C 390.3, NGC 4151, and NGC 5548, are presented. We analyze the H$α$ and H$β$ profile variations during the monitoring period and study different details (as bumps, absorption bands) which can indicate structural changes in the Broad Line Region (BLR). The BLR dimensions are estimated using the time lags between the continuum and the broad lines flux variations. We find that in the case of 3C 390.3 and NGC 5548 a disk geometry can explain both the broad line profiles and their flux variations, while the BLR of NGC 4151 seems more complex and is probably composed of two or three kinematically different regions.

astro-ph.GA↗

arXiv2009

The line parameters and ratios as the physical probe of the line emitting regions in AGN

Here we discuss the physical conditions in the emission line regions (ELR) of active galactic nuclei (AGN), with the special emphasize on the unresolved problems, e.g. the stratification of the Broad Line Region (BLR) or the failure of the photoionization to explain the strong observed optical Fe II emission. We use here different line fluxes in order to probe the properties of the ELR, such as the hydrogen Balmer lines (Ha to He), the helium lines from two subsequent ionization levels (He II 4686 and He I 5876) and the strongest Fe II lines in the wavelength interval 4400-5400 Å. We found that the hydrogen Balmer and helium lines can be used for the estimates of the physical parameters of the BLR, and we show that the Fe II emission is mostly emitted from an intermediate line region (ILR), that is located further away from the central continuum source than the BLR.

astro-ph.GA↗

arXiv2007

Probing the physical properties of the NGC 5548 Broad Line Region using Balmer lines

We investigate the physical characteristics of the Broad Line Region (BLR) of NGC 5548 using the Boltzmann plot (BP) method, that we applied on the Balmer lines observed from 1996 to 2004. We find that variability earlier detected in the lines, is also present in the temperature parameter A, obtained from the BP method. Using the BP temperature parameter A to calculate temperature, we find that the average temperature for the considered period was T$\approx$ 10000 K, and that varies from 5000 K (in 2002) to 15000 K (in 1998). This variation correlates with the AGN-component of the optical continuum flux (r=0.85) and may indicate the existence of an accretion disc in the BLR of NGC 5548.

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arXiv2007

The Sigma-D Relation for Planetary Nebulae: Preliminary Analysis

An analysis of the relation between radio surface brightness and diameter, so-called Sigma-D relation, for planetary nebulae (PNe) is presented: i) the theoretical Sigma-D relation for the evolution of bremsstrahlung surface brightness is derived; ii) contrary to the results obtained earlier for the Galactic supernova remnant (SNR) samples, our results show that the updated sample of Galactic PNe does not severely suffer from volume selection effect - Malmquist bias (same as for the extragalactic SNR samples) and; iii) we conclude that the empirical Sigma-D relation for PNe derived in this paper is not useful for valid determination of distances for all observed PNe with unknown distances.

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arXiv2007

Emitting gas regions in Mrk 493: An extensive Fe II line emission region

We performed 3D spectroscopic observations of Mrk 493 in order to investigate the Fe II emitting region and their possible connection with the Hydrogen emitting region. We found that there is a strong Fe II emission in an extensive region ~ 4" x 4" around Sy 1 nucleus. The Fe II line width indicates that these lines are originated in an intermediate line region.

astro-ph↗

arXiv2006

The flux ratio of the [OIII] 5007,4959 lines in AGN: Comparison with theoretical calculations

By taking into account relativistic corrections to the magnetic dipole operator, the theoretical [OIII] 5006.843/4958.511 line intensity ratio of 2.98 is obtained. In order to check this new value using AGN spectra we present the measurements of the flux ratio of the [OIII] 4959,5007 emission lines for a sample of 62 AGN, obtained from the Sloan Digital Sky Survey (SDSS) Database and from published observations. We select only high signal-to-noise ratio spectra for which the line shapes of the [OIII] 4959,5007 lines are the same. We obtained an averaged flux ratio of 2.993 +/- 0.014, which is in a good agreement with the theoretical one.

astro-ph↗

arXiv2006

Complex emission line region of Mrk 817

In this work we study the physical and kinematical properties of the emission line region of Seyfert 1.5 galaxy Mrk 817 using three sets of observations, among which are high-resolution spectra obtained with the Isaac Newton Telescope on Canary Islands. We find that in Mrk 817 the Narrow (NEL) and Broad Emission Lines (BEL) are very complex, indicating that structure of both the Narrow (NLR) and Broad Line Region (BLR) is complex and consists of at least two sub-regions with different kinematical properties. We find that the BEL can be fitted with the two-component model, where the core of the line is coming from a spherical region with isotropic velocity distribution, and wings might be affected by a low inclined accretion disc (or disc-like emitting region). Also, we discuss the physical properties of the BLR. Moreover, we find that an outflow is present in the NLR, that may be driven by an approaching jet.

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arXiv2004

Contribution of the Disk Emission to the Broad Emission Lines in AGNs: Two-component model

We present an investigation of the structure of the emission line region in a sample of 12 single-peaked Active Galactic Nuclei (AGNs). Using the high resolution H-beta and H-alpha line profiles observed with the Isaac Newton Telescope (La Palma) we study the substructure in the lines (such as shoulders or bumps) which can indicate a disk or disk-like emission in Broad Line Regions (BLRs). Applying Gaussian analysis we found that both kinds of emission regions, BLR and NLR, are complex. In this sample the narrow [OIII] lines are composites of two components; NLR1 which have random velocities from \sim 200 to 500 km/s and systematic velocities toward the blue from 20 to 350 km/s, and NLR2 with smaller random velocities (\sim 100-200 km/s) and a redshift corresponding to the cosmological one. The BLR also have complex structure and we apply a two-component model assuming that the line wings originate in a very broad line region (VBLR) and the line core in an intermediate line region (ILR). The VBLR is assumed to be an accretion disk and the ILR a spherical emission region. The model fits very well the H-alpha and H-beta line profiles of the AGNs.

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arXiv2004

H II emission line region in LEDA 212995, a small neighboring galaxy of Mrk 1040

We present here new spectroscopic observations of Mrk 1040 and LEDA 212995 (Mrk 1040 companion) obtained with the Isaac Newton Telescope (INT). The intensity ratios and widths for the narrow emission lines found in LEDA 212995 are typical of H II regions. The red-shift (0.0169$\pm$0.00015) of the object derived from these emission lines is very close to the red-shift of Mrk 1040 (z=0.01665). The weak narrow and broad absorption lines were detected in the H$α$ wavelength band of LEDA 212995 spectra. These absorptions indicate that the companion might be at least partly obscured by Mrk 1040. Using this and previous observations we discuss the possible physical relationship between these two galaxies.

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arXiv1997

A Note on the Total Absorption Cross-section of Galaxies

In this work we shall sketch a further piece of evidence for the plausibility of hypothesis of galactic origin of Ly-$α$ forest absorption systems. Two basic premises of our discussion are (1) HDF redshift surface densities in the redshift interval 0<z<6; and (2) validity of low-redshift results on redshift coincidences, showing average absorption cross-section corresponding to radius of 160$h^{-1}$ kpc for $L^*$ galaxies. Low-redshift analysis also showed covering factor nearing unity, which will be used and discussed in further considerations. Semantic problems concerned with the interpretation of galaxy absorption cross-section are discussed in some details, and importance of distinction between size of the absorbers and absorption coherence length is emphasized. It is shown that HDF data predict huge number of absorption systems, in fact much larger than observed, which shows frequently quoted argument that number of galaxies is insufficient to account for all absorption lines to be wrong. Road to achieving higher compatibility with the empirical statistics is shown to lie in applying the luminosity scaling, possibly with cut-off. This is significant for recent attempts to explain the association of the Ly-$α$ forest systems with normal galaxies.

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