HI absorption around the nucleus of an active galaxy NGC1052 Yun-da Li Supervisor : Sawada-Satoh, Satoko Shen, Zhiqiang August 28, 2003 ASIAA summer student program

Outline Introduction - source - motivation - observation Result - spectrum, map Discussion - HI distribution, model Summary

Introduction The giant elliptical galaxy NGC1052, which is classified as LINER or seyfert 2 galaxy, hold an AGN in the Center. (Ho et al. 1997) The red shift z = The red shift z = mas corresponds to pc 1 mas corresponds to pc The systemic velocity V sys is 1474 km/s The systemic velocity V sys is 1474 km/s

Previous work: (1) The HI distribution has been mapped at a resolution of 1.8 arcsec with the VLA, using HI emission and absorption. (Gorkon et al., 1985) (2) There are several velocity systems of HI absorption around the nucleus. (Vermeulen et al. 2002)

(3) There is a dense plasma torus around the nucleus. (Kameno et al. 2001, 2003)

Motivation: (1) Confirm the model raised by Kameno et al. (2) Compare the HI absorption region with the previous work.

Observation: VLBI -EVN: The European VLBI Network (EVN) is an interferometric array of radio telescope spread throughout Europe and beyond. 6 antennas are included in this observation.

Observation date: Nov. 14, 2000 Angular resolution: 0.05 × 0.02 (arcsec) P.A.~ 20° Frequency: GHz (for HI absorption and continuum emission) Bandwidth: 8 MHz × 2 Velocity resolution: km/s Data reduction: Fringe fitting + priori calibrations : AIPS Imaging + self-cal. : AIPS

Result HI absorption spectrum.

Use a Two-Gaussian fitting y = m 7 + m 1 × exp[-(x-m 2 ) 2 /m 3 2 ] + m 4 × exp[-(x-m 5 ) 2 /m 6 2 ] systemic velocity 1474

Column density of HI gas Peak velocity (km/s) ∫τdv Column density N HI (atoms/cm 2 ) 1507±41.68±0.35(3.06±0.63)x ±41.36±0.26(2.47±0.47)x * N HI = 1.82 × × T spin × ∫τdv ( Spitzer 1978) ** ∫τdv = τ× ∆v FWHM ; τ= - ln(I/I 0 ) ; ∆v FWHM = 2√(ln2) × w *** A spin temperature of 100K is assumed

Image Contour: continuum map Grey: opacity map Contour: continuum map Grey: opacity map Opacity τ = - ln( I/I 0 ) I > 5σ from higher or lower line map I 0 > 5σ from continuum map Higher velocity 5 pc Lower velocity

What we get There are two velocity systems of HI gas around the nucleus. Both the velocity systems are red-shifted. Both the velocity systems are red-shifted. The two velocity systems show similar opacity distribution. The two velocity systems show similar opacity distribution. HI Absorption happens ahead of the central region and the western jet. HI Absorption happens ahead of the central region and the western jet. HI gas distributes about 100 mas along the jet axis. HI gas distributes about 100 mas along the jet axis.

Confirm the model (Kameno et al. 2001)

Summary Two velocity systems of HI absorption are detected. We obtain the first high resolution map of HI absorption near by the nucleus of NGC1052. We obtain the first high resolution map of HI absorption near by the nucleus of NGC1052. Our result can agree Kameno’s model Our result can agree Kameno’s model bservation with more sensitive and higher angular resolution to clarify the dynamics of the nuclear region in NGC1052 using the HI absorption. Future work Observation with more sensitive and higher angular resolution to clarify the dynamics of the nuclear region in NGC1052 using the HI absorption.

Thanks everyone Especially, Satoko and Dr. Zhen !!