J. J. Perry’s scientific contributions

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Publications (5)


Circum-nuclear gas flows in NGC 4151.
  • Article
  • Full-text available

September 1995

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40 Reads

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3 Citations

Astronomy and Astrophysics

B. Vila-Vilaro

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A. Robinson

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[...]

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C. N. Tadhunter

We report broad-band imaging observations which reveal a circum-nuclear gas ring in NGC 4151. The ring is delineated by two arc-like features probably resulting from dust extinction of the background stellar continuum. These features are distributed along opposite quadrants of an elliptical ring which has a semi-major axis of length 1.8kpc and is approximately aligned with the NE-SW axis of elongation of the extended emission line region. We discuss this ring in relation to the spatial distribution and kinematics of both ionized and neutral gas components as revealed by published optical spectroscopy and 21-cm observations. These data allow us to form a coherent picture of the gas flows in the circum-nuclear environment of NGC 4151 which is strikingly similar to numerical simulations of streaming induced by barred potentials in which the x2 family of orbits is well developed. On this basis, we propose that the distribution of gaseous material in the galactic bar of NGC 4151 traces the path by which the gas is transported towards the active nucleus. The alignment between the circum-nuclear ring and the ENLR can then be seen as a strong indication that the collimation of the ionizing radiation field of the active nucleus is related to the dynamical parameters of the galactic bar. Specifically, we propose that bar-driven gas flows create the opaque torus which is believed to collimate the radiation field.

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Hysteresis in broad-line regions of active galactic nuclei

December 1994

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19 Reads

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10 Citations

Monthly Notices of the Royal Astronomical Society

The response of emission-line luminosities to changes in the observed continuum in active galaxies is commonly used for reverberation mapping (RM) of the emission-line region. The method assumes regularity in the continuum source and linearity in the line response to the continuum, and that the phase-space distribution of the line-emitting gas is constant in time. The wealth of information contained in the detailed line profiles is under-utilized in current methods of RM. We propose a new method to improve this situation. We define normalized profiles and show how their use enables one to explore details of the emission-line region that have hitherto eluded detection. Furthermore, we investigate the possibility of testing the validity of the assumptions as used in the standard application of RM. We present new methods, the hysteresis test and the Q concept - also based on the line profiles - to test the basic assumptions of RM. The test falls when applied to NGC 4151. We show that there is good evidence either for significantly extended and complex emission-line regions, or for changes in the mass distribution over time-scales of months or more - i.e. on time-scales comparable to the length of typical observing campaigns. We discuss the implication of our results.


Hysteresis in Broadline Regions of Active Galactic Nuclei

November 1994

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20 Reads

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12 Citations

Monthly Notices of the Royal Astronomical Society

The response of emission-line luminosities to changes in the observed continuum in active galaxies is commonly used for reverberation mapping (RM) of the emission-line region. The method assumes regularity in the continuum source and linearity in the line response to the continuum, and that the phase-space distribution of the line-emitting gas is constant in time. The wealth of information contained in the detailed line profiles is under-utilized in current methods of RM. We propose a new method to improve this situation. We define normalized profiles and show how their use enables one to explore details of the emission-line region that have hitherto eluded detection. Furthermore, we investigate the possibility of testing the validity of the assumptions as used in the standard application of RM. We present new methods, the hysteresis test and the Q concept - also based on the line profiles - to test the basic assumptions of RM. The test falls when applied to NGC 4151. We show that there is good evidence either for significantly extended and complex emission-line regions, or for changes in the mass distribution over time-scales of months or more - i.e. on time-scales comparable to the length of typical observing campaigns. We discuss the implication of our results.


Monitoring of active galacitc nuclei. 4: The Seyfert 1 galaxy NGC 4593

March 1994

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30 Reads

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2 Citations

Astronomy and Astrophysics

Results of a five-month campaign of optical monitoring the Seyfert 1 galaxy NGC 4593 are presented. High resolution H-alpha and H-Beta spectra and direct images in the Johnson U, B, V, R, and I bands were obtained between January and June 1990. The emission lines and the continuum showed strong variations on time scales of weeks to days. The H-alpha line varied by more than 30% within only 5 days. Cross-correlating the light curves of the Balmer lines with that of the optical continuum gives a lag of around 4 days. Therefore, this low luminosity Seyfert galaxy may have one of the smallest broad line regions (BLRs) known so far.


Spectroscopic monitoring of active galactic nuclei. II - The Seyfert-1 galaxy NGC 3516

February 1993

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69 Reads

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6 Citations

Astronomy and Astrophysics

We present results of a five month spectroscopic monitoring campaign of the Seyfert-1 galaxy NGC 3516. Using a new calibration method and applying a correction for seeing differences during the various observations we can scale the spectra to each other with a much higher accuracy than hitherto achieved. NGC 3516 shows large amplitude variations on a time scale of several weeks. Asymmetric profile variations occur on the same time scale as the continuum variations. We show the presence of a varying dip on the blue wing of the H-beta profile, which is not present on the H-alpha profile, and which corresponds to the absorption features previously seen in the UV emission lines of NGC 3516. From cross-correlation analysis we find a time lag of 14 +/- 2 days for the H-alpha and 7 +/- 3 days for the H-beta emission-line response to continuum variations.

Citations (4)


... It may also depend on the previous continuum history and show effects of hysteresis: even if the flux is the same, the line profile may vary depending on whether the source was previously in a higher or lower flux state (e.g. Perry, van Groningen & Wanders 1994). ...

Reference:

Modelling the AGN broad line region using single-epoch spectra – I. The test case of Arp 151
Hysteresis in broad-line regions of active galactic nuclei

Monthly Notices of the Royal Astronomical Society

... We therefore expect the measured lags of the emission lines and their profile shapes to depend on the luminosity state of the continuum ( § 3.3 & § 3.4). We note that unless the velocity field is self-similar in radius (Goad et al. 1999), a profile shape that depends on the continuum luminosity state fails a hysteresis test (see Wanders 1994;Perry, van Groningen, & Wanders 1994). This is true without invoking a redistribution of material within the BLR or other geometrical effects as suggested by Wanders & Peterson (1996). ...

Hysteresis in Broadline Regions of Active Galactic Nuclei

Monthly Notices of the Royal Astronomical Society

... In addition, the maxima and minima of the light curves appear to have statistically symmetrical shapes (seeFigure 1c), but this property should be investigated more thoroughly. July 18, 1997 13:32 Annual Reviews AR037-12Salamanca et al 1994, Winge et al 1995) NGC 3516 t d ∼ 7 days (Wanders et al 1993) NGC 3783 t d ∼ 8 days while t d of C IV was 5 days in the same period (Stripe et al 1994, Reichert et al 1994) PG 0804+762 t d ∼ 93 days (Kaspi et al 1996b) PG 0953+414 t d ∼ 110 days (Kaspi et al 1996b) a t: interval of time between successive maximum and minimum. b t d : time delay between the UV lines and UV continuum or between optical lines and optical continuum variations. ...

Spectroscopic monitoring of active galactic nuclei. II - The Seyfert-1 galaxy NGC 3516

Astronomy and Astrophysics

... Many observational studies provided evidence of such gaseous streaming in a barred potential (e.g. Vila-Vilaro et al., 1995;Koribalski et al., 1996;Jogee et al., 2005). However, a single large-scale bar cannot transport gas below a few hundreds parsecs where the gas accumulates after crossing the ILR. ...

Circum-nuclear gas flows in NGC 4151.

Astronomy and Astrophysics