Download Investigating the relationship between the Optical and HI diameter of

Investigating the relationship
between the HI and optical diameter
of a sample of LVHIS galaxies
Nicolette Pekeur (UCT)
Supervisors:
Prof. Renee Kraan-Korterweg (UCT), Prof. Erwin de Blok (UCT) and Dr.
Baerbel Koribalski (ATNF)
Outline

Introduction

Sample Definition

Aim

Results & Conclusions

Summary

Future Prospects
Introduction
 Not clear how small-scale galaxy processes determine the
large-scale structure of a galaxy. Not even clear how Mpc
environment is correlated with the kpc HI disk.
 Examining how the HI disk of a galaxy depends on various
galaxy properties, presents a first step towards
understanding how it is formed.
Sample definition
 Subsample of the Local Volume HI Survey (LVHIS;
Koribalski et al., 2008).
 HI selected (HIPASS; Barnes et al., 2001) All
morphological types.
 Volume-limited (D≤10 Mpc-LV; dwarf galaxies).
 Observations with ATCA sensitivity ~1 mJy and
resolution ~1’.
 Motivation:
 Test previous studies that selects against faint galaxies.
 Pilot study.
Aim
 Investigate the relationship between the HI and optical
diameter of 19 galaxies from LVHIS.
 The HI diameter is also correlated with the HI mass, HI massto-light ratio and environment.
Results
 HI properties were obtained at 3 HI column density
levels (NHI=2.5E19 (~3σ), 8.0E19 and 2.5E20 cm2). Only
review results obtained for the outermost HI diameter
(NHI=2.5E19 cm-2).
 HI- vs. Optical Diameter
 HI Mass
 HI Mass-to-Light Ratio
HI Diameter vs. Optical Diameter
 The HI diameter (DHI) measured at NHI=2.5E19 cm-2.
 Optical diameter (Dopt), defined at μB=25 and 26 mag
arcsec-2, D25B and D26B.
log(DHI)=0(.55 ±0.13)log(D25B)+(1.48±0.29)
log(DHI)=(0.66±0.21)
log(D26B)+(1.11±0.52)
Conclusion I
 The HI and optical diameter is strongly correlated.
 DHI> Dopt for all galaxies.
NHI (cm-2)
μB (mag arcsec-2)
DHI/Dopt
Sample
2.5×1019
25
3.2±0.5
LVHIS
1.25×1020
25
3.3±1.5
WHISP1
2.5×1019
26
2.0±0.3
LVHIS
1019
26.5
2.4±0.1
FIGGS2
References:
1. Swaters et al. (2002) The Westerbork HI Survey of Spiral and Irregular galaxies I.
2. Begum et al. (2008) FIGGS: Faint Irregular Galaxies GMRT SurveyOverview, Observations and First Results
HI Mass vs. HI Diameter
 Examine the HI mass (MHI) as a function of HI diameter
by computing the HI mass inside the diameter.
log (MHI) = (2.00±0.16) log(DHI)+(6.15 ±0.18)
Conclusion II
 HI mass is proportional to the square of the HI diameter.
 The fitted relation is,
 log(MHI)=(2.00±0.16) log(DHI)+(6.15±0.18)
 FIGGS galaxies,
 log(MHI)=(1.99±0.11) log(DHI)+(6.08±0.06)
 MHI α D2HI  the HI surface density is constant when it is
averaged over the HI disk.
 ΣHI=(1.8±0.2) M pc-2
 Spread in ΣHI is due to local density variations 
presence of a central bar (~60%).

HI mass-to-light ratio
 Measures the relative amounts of HI gas and stars
(relative HI content).
 Comparing the relative HI content with the HI-to-optical
diameter ratio determine effect of star formation and
the star formation rate on the HI diameter.
Relative HI content vs. HI-tooptical diameter ratio
Conclusion III
 More extended galaxies have higher HI mass-to-light
ratios.
MHI/LB (solar units)
Sample
0.9±0.2
LVHIS
1.5
WHISP1
5.0
FIGGS2
References:
1. Swaters et al. (2002) The Westerbork HI Survey of Spiral and Irregular galaxies I.
2. Begum et al. (2008) FIGGS: Faint Irregular Galaxies GMRT SurveyOverview, Observations and First Results
Summary
 Results agree with literature.
 Pilot study LVHIS data is reliable.
 What are the HI properties of all LVHIS galaxies?
(Koribalski et al., 2008/2009)
Future Prospects
 HI properties of all LVHIS galaxies means:
 Reduce statistical error increasing the sample size.
 Majority of galaxies studied here, are late-type galaxies.
Expand our results to all morphological types (with
detectable HI).
 Definitive results for environmental effects.
 Most of the galaxies are isolated.
 MeerKAT and ASKAP much more complete LV census.
Estimated increase in the number of LV members, ~4
times the current known value (Staveley-Smith, 2008).
Future Prospects (cont.)
 R-band optical diameter instead of B-band optical
diameter.
Thank You