The Fate of the Neutral Gas in Group Environments

Transcription

1 The Fate of the Neutral Gas in Group Environments Tobias Westmeier (ICRAR / UWA) International Centre for Radio Astronomy Research

2 Collaborators HIPASS 2 Parkes survey SoFiA Busy Function M. Calabretta R. Jurek B. S. Koribalski M. Meyer A. Popping L. Staveley-Smith I. Wong B. S. Koribalski M. Meyer A. Musaeva D. Obreschkow A. Popping A. Wright T. Young H. Courtois L. Flöer N. Giese J. M. van der Hulst R. Jurek B. S. Koribalski M. Meyer A. Popping P. Serra L. Staveley-Smith B. Winkel R. Jurek B. S. Koribalski D. Obreschkow L. Staveley-Smith Ram pressure S. Haan NGC 55 / 300 R. Braun B. S. Koribalski 2

3 Motivation 3

4 Motivation H Ⅰ deficiency in groups and clusters Solanes et al. (2001) Hess & Wilcots (2013) Increases towards group centre Increases with group size 4

5 Motivation Gas stripping in high-density environments HCG 44 (Serra et al. 2013) Removal of neutral gas through Tidal interaction Ram-pressure stripping Effect on HIMF and star formation Kenney et al. (2004) Kilborn et al. (2006) NGC 4522 NGC 3783 group 5

6 Observations and Data 6

7 Observations and Data HIPASS 2 σrms 4.8 mjy (at 26.4 km/s) Deep Parkes survey MH Ⅰ M [d / 5 Mpc]2 (10 σ at 26.4 km/s) NH Ⅰ cm 2 (5 σ at 26.4 km/s) Deep Parkes H Ⅰ survey σrms 11 mjy (at 1.6 km/s) MH Ⅰ M [d / 5 Mpc]2 (10 σ at 20 km/s) NH Ⅰ cm 2 (5 σ at 20 km/s) 7

8 SoFiA Source Finding Application (SoFiA) New 3D source finding pipeline Graphical user interface Novel algorithms created for H Ⅰ surveys Smooth + clip finder Reliability calculation Busy Function 2D 1D wavelet finder CNHI finder (Serra et al. 2012, PASA, 29, 296) (Serra et al. 2012, PASA, 29, 296) (Westmeier et al. 2014, MNRAS, 438, 1176) (Flöer et al. 2012, PASA, 29, 244) (Jurek 2012, PASA, 29, 251) Download SoFiA GitHub: Wiki, documentation, bug reports, feature requests Paper Serra, Westmeier, et al., submitted to MNRAS 8

9 The Busy Function The Busy Function B(x) = (a / 4) [erf(b₁ (w + x xe)) + 1] [erf(b₂ (w x + xe)) + 1] [c (x xp)n + 1] Purpose Fit double-horn profiles of galaxies Measure galaxy parameters: line width, peak flux, integrated flux, radial velocity, etc. More accurate than direct measurements, in particular for peak flux and line width Paper Westmeier et al., 2014, MNRAS, 438, 1176 Fitting software BF_dist busyfit ( written by Russell Jurek) ( 9

10 Observations and Data Galaxies detected HPBW 31 H Ⅰ detections N247 v = km/s d = 2 15 Mpc log(mh Ⅰ / M ) = N45 N detections not in HIPASS 5 due to velocity limit 8 new H Ⅰ detections of dwarf galaxies NGC 59 (Beaulieu et al. 2006) All H Ⅰ detections have (tentative) optical counterpart in DSS / GALEX No intergalactic gas / dark galaxies N300 N55 10

11 Observations and Data New H Ⅰ detections MH Ⅰ 10⁸ M compact irregular not much data available (photometric, spectroscopic) Images: DSS 11

12 Results 12

13 Results H Ⅰ mass vs. distance MH Ⅰ 10⁷ M Fairly even spread of galaxies across mass range 13

14 Results Comparison with H Ⅰ mass function Schechter function Θ(m) dm = Θ mα exp( m) dm where m MH Ⅰ / M MH Ⅰ H I Zwaan et al. (2005) Global HIPASS H Ⅰ mass function α = 1.37 log(m MH Ⅰ H I / M ) = 9.80 Θ =

15 Results Comparison of simulation and observation Too many high-mass galaxies MH Ⅰ 109 M Too few intermediate-mass galaxies Model 1 MH Ⅰ M Similar result for ALFALFA HIMF (Martin et al. 2010) Is this result significant? Model 2 Observation 15

16 Results Comparison of simulation and observation Kolmogorov Smirnov test Cumulative H Ⅰ mass distribution Results D 0.17 p 31% The chance of a statistical fluctuation creating a discrepancy greater than the one observed is 31% if model and observation were drawn from the same H Ⅰ mass function. Discrepancy not statistically significant due to small sample size. 16

17 Discussion 17

18 Discussion Reason for lack of low-mass galaxies? Based on data from Grcevich & Putman (2009) Environmental effects Tidal interaction and accretion Ram-pressure stripping Internal effects (SF & AGN) Ionisation of neutral gas Ejection of gas Local Group H Ⅰ deficiency in dwarf galaxies (Grcevich & Putman 2009) Quenching of star formation Ram-pressure stripping? 18

19 Discussion Reason for lack of low-mass galaxies? Based on data from Grcevich & Putman (2009) Environmental effects Tidal interaction and accretion Ram-pressure stripping Internal effects (SF & SNe) Ionisation of neutral gas Ejection of gas Local Group H Ⅰ deficiency in dwarf galaxies (Grcevich & Putman 2009) Quenching of star formation Ram-pressure stripping? Slater & Bell (2014) 19

20 Discussion Ram pressure: NGC 55 Studies hampered by disc inclination ( 80 ) Asymmetric H Ⅰ disc NH Ⅰ profile NH Ⅰ map Westmeier et al. (2013) 20

21 Discussion Ram pressure: NGC 300 Again asymmetric H Ⅰ disc velocity map NH Ⅰ map NH Ⅰ profile Westmeier et al. (2011) 21

22 Discussion Ram pressure: NGC 300 Again asymmetric H Ⅰ disc Ram pressure significant at R 15 kpc gravity dominates gravity dominates ram pressure dominates ram pressure dominates Westmeier et al. (2011) 22

23 Discussion Ram pressure: NGC 300 perpendicular Again asymmetric H Ⅰ disc Ram pressure significant at R 15 kpc Kinematic signature velocity velocity map residual (parallel) parallel S. Haan Haan & Braun (2014) 23

24 Discussion Outlook: systematic study of ram pressure in Sculptor galaxies NGC 55 NGC 247 NGC 300 NGC 7793 Use galaxies as probes to determine density of IGM measure 3D motions of galaxies Determine role of ram pressure in removal of neutral gas impact on star formation history 24

25 Summary 25

26 Summary Deep H Ⅰ survey of Sculptor group region 31 H Ⅰ detections, 8 entirely new, no dark galaxies Comparison with H Ⅰ mass function Too many galaxies with MH Ⅰ 10⁹ M, too few with MH Ⅰ 10⁷ ⁸ M Discrepancies not statistically significant due to small sample size ASKAP / Apertif and SKA 1 Survey needed Ram-pressure effects in groups Evidence for ram pressure in Sculptor group morphological + model of Haan & Braun (2014) nigm cm 3 Ram pressure important for galaxy evolution in groups Missing satellites problem might be an illusion 26

27 Motivation Impact on H Ⅰ mass function Steeper in high-density environments low-density environments Springob et al. (2005) (Zwaan et al. 2005) (Springob et al. 2005) Zwaan et al. (2005) 27

28 Motivation Deep H Ⅰ survey of Sculptor group Nearby H Ⅰ mass sensitivity < 10⁷ M High spatial resolution But: large area on the sky C/2012 F6 (Lemmon) NGC 300 NGC 253 NGC 55 C/2011 L4 (PANSTARRS) 28

29 Results Simulation of HIPASS H Ⅰ mass function Assumptions Homogeneous distribution of galaxies Random mass of 6 < log(mh Ⅰ / M ) < 10 following HIPASS Schechter function Random orientation ( inclination) H Ⅰ line width from global HIPASS Δv MH Ⅰ relation Random distance of 2 < d < 15 Mpc (taking survey geometry into account) Calculate SNR and keep detectable galaxies Duffy et al. (2012) SNR > 10 29

30 Results Comparison with Springob et al. (2005) high dens ity: Environmental effect on HIMF Low-density HIMF (n < 1.5) α = 1.24 α = 1.38 log(m MH Ⅰ H I / M ) = High-density HIMF (n > 3.0) low d ensit y: α α = 1.24 log(m MH Ⅰ H I / M ) = 9.95 = 1.38 Results Low density: p = 43% Med. density: p = 8.5% High density: p = 21% Springob et al. (2005) 30

31 Observations and Data Peak flux density maps HPBW HIPASS 2 Parkes survey NGC 247 NGC 45 NGC 253 HPBW 31

32 Discussion Ram pressure Ram pressure: Pram = ϱ v2 Gravitational pressure: Pgrav = Σgas(r) Φ(r) / z max Face-on situation, but accurate for inclination angles of up to 60 (Rödiger et al. 2005) gravitational pressure gas disc DM halo Westmeier et al. (2011) ram pressure 32