HI absorption around the nucleus HI absorption around the nucleus of an active galaxy NGC1052of an active galaxy NGC1052

Yun-da LiYun-da Li

Supervisor : Sawada-Satoh, SatokoSupervisor : Sawada-Satoh, Satoko Shen, Zhiqiang 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 isThe giant elliptical galaxy NGC1052, which isclassified as LINER or seyfert 2 galaxy, hold anclassified as LINER or seyfert 2 galaxy, hold anAGN in the Center. (Ho et al. 1997)AGN in the Center. (Ho et al. 1997)

The red shift z = 0.0049The red shift z = 0.0049 1 mas corresponds to 0.095 pc1 mas corresponds to 0.095 pc The systemic velocity VThe systemic velocity Vsys sys is 1474 km/sis 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: 1.420 GHz (for HI absorption and continuum emission)• Bandwidth: 8 MHz × 2• Velocity resolution: 3.125 km/s

Data reduction:

• Fringe fitting + priori calibrations : AIPS

• Imaging + self-cal. : AIPS

ResultHI absorption spectrum.

Use a Two-Gaussian fitting

y = m7 + m1 × exp[-(x-m2)2/m32] + m4 × exp[-(x-m5)2/m6

2]

systemic velocity

1474

Column density of HI gas

Peak velocity (km/s) ∫τdv Column density NHI (atoms/cm2)

1507±4 1.68±0.35 (3.06±0.63)x 1020

1645±4 1.36±0.26 (2.47±0.47)x 1020

* NHI = 1.82 × 1018 × Tspin × ∫τdv ( Spitzer 1978)

** ∫τdv = τ× ∆vFWHM ; τ= - ln(I/I0) ; ∆vFWHM = 2√(ln2) × w

*** A spin temperature of 100K is assumed

Image

Contour: continuum mapGrey: opacity map

Contour: continuum mapGrey: opacity map

Opacity τ = - ln( I/I0)I > 5σ from higher or lower line mapI0 > 5σ from continuum map

Higher velocity

5 pc 5 pc

Lower velocity

What we get There are two velocity systems of HI gas around theThere are two velocity systems of HI gas around the nucleus. nucleus. Both the velocity systems are Both the velocity systems are red-shiftedred-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 andHI Absorption happens ahead of the central region and the western jet. 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 HIWe obtain the first high resolution map of HI

absorption near by the nucleus of NGC1052. absorption near by the nucleus of NGC1052.

Our result can agree Kameno’s modelOur result can agree Kameno’s model

Future work Observation with bservation with more sensitivemore sensitive and and higher angularhigher angular resolution resolution to clarify the dynamics of the nuclear region in to clarify the dynamics of the nuclear region in NGC1052 using the HI absorption. NGC1052 using the HI absorption.

Thanks everyone

Especially, Satoko and Dr. Zhen !!