Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userGemini Imaging of Mid-IR Emission from the Nuclear Region of Centaurus A
148
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
We present high spatial resolution mid-IR images of the nuclear region of NGC 5128 (Centaurus A). Images were obtained at 8.8 micron, N-band (10.4 micron), and 18.3 micron using the mid-IR imager/spectrometer T-ReCS on Gemini South. These images show a bright unresolved core surrounded by low-level extended emission. We place an upper limit to the size of the unresolved nucleus of 3.2 pc (0.19) at 8.8 micron and 3.5 pc (0.21) at 18.3 micron at the level of the FWHM. The most likely source of nuclear mid-IR emission is from a dusty torus and possibly dusty narrow line region with some contribution from synchrotron emission associated with the jet as well as relatively minor starburst activity. Clumpy tori models are presented which predict the mid-IR size of this torus to be no larger than 0.05 (0.85pc). Surrounding the nucleus is extensive low-level mid-IR emission. Previously observed by ISO and Spitzer, this paper presents to date the highest spatial resolution mid-IR images of this extended near nuclear structure. Much of the emission is coincident with Pa-alpha sources seen by HST implying emission from star forming areas, however evidence for jet induced star formation, synchrotron emission from the jet, a nuclear bar/ring, and an extended dusty narrow emission line region is also discussed.
rate research
Read More
We use published mid-IR and V-band flux ratios for images A and B of Q2237+0305 to demonstrate that the size of the mid-IR emission region has a scale comparable to or larger than the microlens Einstein Radius (ER, ~10^17 cm for solar mass stars). Q2237+0305 has been monitored extensively in the R and V-bands for ~15 years. The variability record shows significant microlensing variability of the optical emission region, and has been used by several studies to demonstrate that the optical emission region is much smaller than the ER for solar-mass objects. For the majority of the monitoring history, the optical flux ratios have differed significantly from those predicted by macro-models. In contrast, recent observations in mid-IR show flux ratios similar to those measured in the radio, and to predictions of some lens models, implying that the mid-IR flux is emitted from a region that is at least 2 orders of magnitude larger than the optical emission region. We have calculated the likeli-hood of the observed mid-IR flux ratio as a function of mid-IR source size given the observed V-band flux ratio. The expected flux ratio for a source having dimensions of ~1 ER is a sensitive function of the macro model adopted. However we find that the probability of source size given the observed flux ratios is primarily sensitive to the ratio of the macro-model magnifications. The majority of published macro models for Q2237+0305 yield a flux ratio for images B and A of 0.8 - 1.1. By combining probabilities from the ratios A/B and C/D we infer that the diameter of a circular IR emission region is >1ER with >95% confidence. For microlensing by low-mass stars, this source size limit rules out non-thermal processes such as synchrotron as mechanisms for mid-IR emission.
We present subarcsecond resolution mid infrared images of NGC 4151 at 10.8 micron and 18.2 micron. These images were taken with the University of Florida mid-IR camera/spectrometer OSCIR at the Gemini North 8-m telescope. We resolve emission at both 10.8 micron and 18.2 micron extending ~ 3.5 across at a P.A. of ~ 60 degrees. This coincides with the the narrow line region of NGC 4151 as observed in [OIII] by the Hubble Space Telescope. The most likely explanation for this extended mid-IR emission is dust in the narrow line region heated by a central engine. We find no extended emission associated with the proposed torus and place an upper limit on its mid-IR size of less than or equal to ~ 35 pc.
We present diffraction limited, 10um imaging polarimetry data for the central regions of the archetypal Seyfert AGN, NGC1068. The position angle of polarization is consistent with three dominant polarizing mechanisms. We identify three distinct regions of polarization: (a) north of the nucleus, arising from aligned dust in the NLR, (b) south, east and west of the nucleus, consistent with dust being channeled toward the central engine and (c) a central minimum of polarization consistent with a compact (<22pc) torus. These observations provide continuity between the geometrically and optically thick torus and the host galaxys nuclear environments. These images represent the first published mid-IR polarimetry from an 8-m class telescope and illustrate the potential of such observations.
We report the detection of a 22GHz water maser line in the nearest (D~3.8Mpc) radio galaxy Centaurus A using the Australia Telescope Compact Array (ATCA). The line is centered at a velocity of ~960kms-1, which is redshifted by about 400kms-1 from the systemic velocity. Such an offset, as well as the width of ~120kms-1, could be consistent with either a nuclear maser arising from an accretion disk of the central supermassive black hole, or for a jet maser that is emitted from the material that is shocked near the base of the jet in Centaurus,A. The best spatial resolution of our ATCA data constrains the origin of the maser feature within <3pc from the supermassive black hole. The maser exhibits a luminosity of ~1Lo, which classifies it as a kilomaser, and appears to be variable on timescales of months. A kilomaser can also be emitted by shocked gas in star forming regions. Given the small projected distance from the core, the large offset from systemic velocity, as well as the smoothness of the line feature, we conclude that a jet maser line emitted by shocked gas around the base of the AGN is the most likely explanation. For this scenario we can infer a minimum density of the radio jet of ~>10cm-3, which indicates substantial mass entrainment of surrounding gas into the propagating jet material.
We present an imaging and spectral analysis of the nuclear region of the ULIRG merger Arp 220, using deep textit{Chandra}-ACIS observations summing up to (sim 300mbox{ ks}). Narrow-band imaging with sub-pixel resolution of the innermost nuclear region reveals two distinct Fe-K emitting sources, coincident with the infrared and radio nuclear clusters. These sources are separated by 1 ((sim 380) pc). The X-ray emission is extended and elongated in the eastern nucleus, like the disk emission observed in millimeter radio images, suggesting starburst dominance in this region. We estimate Fe-K equivalent width (gtrsim 1) keV for both sources, and observed 2-10 keV luminosities (sim 2times{10}^{40}mbox{ erg}mbox{ s}^{-1}) (W) and (sim 3 times {10}^{40}mbox{ erg}mbox{ s}^{-1}) (E). In the 6-7 keV band the emission from these regions is dominated by the 6.7 keV Fe textsc{xxv} line, suggesting contribution from collisionally ionized gas. The thermal energy content of this gas is consistent with kinetic energy injection in the interstellar medium by Type II SNe. However, nuclear winds from hidden AGN ((varvsim 2000 mbox{ km}mbox{ s}^{-1})) cannot be excluded. The (3sigma) upper limits on the neutral Fe-K(alpha) flux of the nuclear regions correspond to intrinsic AGN 2-10 keV luminosities (< 1times {10}^{42}mbox{ erg}mbox{ s}^{-1}) (W) and (< 0.4times {10}^{42}mbox{ erg}mbox{ s}^{-1}) (E). For typical AGN SEDs the bolometric luminosities are (< 3times {10}^{43}mbox{ erg}mbox{ s}^{-1}) (W) and (< 8times {10}^{43}mbox{ erg}mbox{ s}^{-1}) (E), and black hole masses (<1times{10}^5 M_{astrosun}) (W) and (< 5times{10}^5 M_{astrosun}) (E) for Eddington limited AGNs with a standard 10% efficiency.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
