PoS(PRA2009)051 rcular http://pos.sissa.it/ axy NGC 2915 moment maps for I ce. s treated as a rotating, expanding t of the Southern Hemisphere ex- ss are expelling the gas from laxy evolution - PRA2009 rmed, would be the first such evidence ed. The central gas dynamics are con- ag X3, Rondebosch 7701, South morphology and kinematics of NGC 2915. We also I ive Commons Attribution-NonCommercial-ShareAlike Licen distributions and kinematics. The presence of large non-ci I synthesis observations of the nearby blue compact dwarf gal I Nearby Survey are presented. High resolution H I , W. J G. de Blok, R. C. Kraan-Korteweg ∗ [email protected] Results from new H Speaker. tension of the H carried out on the Australian Telescope Compact Array as par of a low-mass system. find intriguingevidence for a gas infall event which, if confi sistent with the simple scenario in which winds from high-ma gas torus is able to reproduce the inner H velocity components within the gas at inner radii are reveal the centre of the galaxy. A model in which the central region i the galaxy reveal complex H ∗ Copyright owned by the author(s) under the terms of the Creat c E. C. Elson Our changing view of the blue2915 compact dwarf NGC Department of Astronomy, University of CapeAfrica Town, Private B E-mail:

Panoramic : Wide-field 1-2 GHzJune research on 02 ga - 05 2009 Groningen, the Netherlands PoS(PRA2009)051 I . The ′′ 2 . E. C. Elson 18 data cube by of the galaxy × I data cube. The ′′ disk with well- I I escope Compact Array ing all 6 antennas between and 1.5C runs was approxi- l., 2004) blue compact dwarf 100 hours worth of on-source ey showed that NGC 2915 is ted from the H ration. Archival data obtained line profiles. Rather than con- I ∼ data from the correlator through to vel, had a size of 17 5 an ideal candidate for dark matter atter distribution of a dirty image was deconvolved using dy the gas dynamics of this galaxy n components was convolved with a y fitting and subtracting a first order uv measured the average formation . The channel maps will be presented led two dominant stellar populations, ur observations. Details of the results al of he H high-mass , surrounded ass stellar population to the central H 1 star formation in the outer parts. The and compact dark matter core. re used to produce an H − Nearby Galaxy Survey (THINGS, Walter ng the spiral structure of the outer disk of data were mapped to the image plane. All I morphology of the galaxy. In particular, an velocity field from the first moments of the I uv I . The noise in a line-free channel is Gaussian 1 − 2 0.6 mJy beam ∼ σ -band scale lengths), low surface brightness H B 22 . Interesting is the observation that the stellar component 1 ∼ − yr ⊙ synthesis observations of NGC 2915 using the Australian Tel 0.05 M I ∼ total intensity and velocity dispersion maps were construc I NGC 2915 was observed with 6 different ATCA configurations us The MIRIAD software package was used to take the raw New H H NGC 2915 is classified as a nearby (3.78 Mpc, Karachentsev et a 23 October 2006 and 2mately June 12 2007. hours Each long of while theby 24 Meurer EW-352, hours 750D, et were 1.5B al. spent (1996) were in also the incorporated 6A yielding configu a tot 2. Data acquisition and reduction effort is made to link the energymorphology output which, of for the the central first high-m time,will is be clearly presented resolved by by Elson o et al. in prep. in detail. Previous investigators have focusedNGC on 2915. explaini In this work we focus on the innermost H et al., 2008) have been carried out. These data are used to stu structing a conventional intensity-weighted-mean H data. as part of the Southern Hemisphere extension of The H the image analysis stage. Standard reduction techniques we defined spiral structure, but withabsence of apparently stars no in the significant outer diskstudies. does, however, Meurer make NGC et 291 al. (1996)by were mass-modeling the first the to observed studydark-matter-dominated rotation the at dark curve nearly all m of radii NGC with a 2915. very dense Th in Elson et al. in prep. calculating the zeroth and second moments respectively of t galaxy. Photometry carried out by Meurera et compact al. blue (1994) stellar revea core,by which is a the diffuse, location older of stellarrate current to population. be Meurer et al. (1994) Our changing view of the blue compact dwarf NGC 2915 1. Introduction is embedded in a huge ( a Steer Clean algorithm (SteerGaussian et approximation al., of 1984). the dirty Each beam of which, the at clea the 50% le of our data cubes were produced using natural weighting. The source data were calibrated andpolynomial then to continuum the subtracted line-free b channels. The remaining distributed with a standard deviation of channel width of the final data cube is 3.5 km s PoS(PRA2009)051 km mass of I E. C. Elson rent absence disk. Clearly over-densities inally, Bureau I I al H moment maps are pre- velocity field. I I s. nsity map the total H aint stellar population. The gas ks at inner radii are indicative of morphology of NGC 2915. Masset long the outer contours are caused sk scenario can adequately account lo. Furthermore, NGC 2915 seems e unlikely that the spiral structure is I psidedness. s possibly non-orthogonal kinematic lar feedback from the young central on the disk by a nearby companion nsity wave is far too inefficient at all at a large fraction of unseen mass is Marel & Franx, 1993) were fitted and xy where we observe ongoing active distortion of the contours suggests the st time. Also noticeable is the plume- contained within the H onstruct an H persion profile yields an average outer ave is triggered by an external perturber. s in the shapes of the iso-velocity contours velocity dispersion map. The highest velocity I 3 m image as well as the H µ . ⊙ spiral morphology. Meurer et al. (1994) carried out deep I M 8 velocity field is displayed in the lower left panel of Fig. 1 I 10 × 5.0 which is close to the fixed gas velocity dispersion value of 11 1 ∼ − of the outer disk is therefore difficult to explain in the appa 1 − morphology but fails to describe the observed kinematics. F 9 km s I ∼ total intensity map (Fig. 1, upper right panel) are two centr 9 km s I ∼ feature located towards the North-West. From the total inte data products I I The SINGS (Kennicutt et al., 2003) 3.6 Several authors have attempted to explain the observed H The lower right panel of Fig. 1 shows the H The 3rd order Gauss-Hermite H used by Leroy et al. (2008) for their sample of THINGS galaxie 1 − Our changing view of the blue compact dwarf NGC 2915 line profiles, 3rd order Gauss-Hermite polynomials (van der the velocities associated with the fitted peaks were used to c 3. H 3.1 Total intensity map the galaxy is estimated to be which our observations are able tolike H clearly resolve for the fir sented in Fig. 1. The diffuse, old stellar population is well & Bureau (2003), using numerical simulations,caused showed by it a to rotating b centralto bar be or isolated. a rotatingcannot The tri-axial be effect invoked. DM It of ha is a thereforeMasset unlikely gravitational that & torque the Bureau spiral exerted w (2003) alsodistributed in investigated the the disk of possibility NGC th 2915.for They the found that observed a H heavy di visible in the H et al. (1999) showed that swingradii to amplification be of able the to spiral sustain the de observed H s imaging of the outer disk of NGC 2915 and found no significant f dispersion of dispersions are seen instar the formation central-most and regions may of thereforestellar the be population. gala due to The the azimuthally effectsdisk of averaged dispersion stel velocity of dis and is clearly one of a rotating disk. The overall “S-shaped” presence of a kinematic warpby within streaming the gas disk. motions Small alongsignificant wiggles non-circular the a gas spiral motions. arms. Finally, difference The sharp kin major and minor axes suggest a certain degree of kinematic lo 3.3 Velocity dispersion map on the receding and approaching halves of the galaxy as well a of stars. 3.2 Velocity field PoS(PRA2009)051 position- (Fig. 2, 1 E. C. Elson nts the edge − (1.83 kpc and 0.9 ′′ 25 km s with the thick contour of the centre of NGC 1 ∼ ′′ − and 54 total intensity map). A ′′ I 150 beard in the position-velocity ∼ I anding gas component. This is eal the presence of non-circular velocity dispersion map. I an H in the H learly lagging in velocity relative to H he high-mass star-forming core. It is y as much as eature of the gas in the galaxy. The C 2915 are often skewed to one side. eft corner represents the half power beam e gas dynamics. sharp velocity spike, shown in the right- s of lengths 100 d it is found to coincide spatially with the 4 Bottom right panel: . 1 − line profiles are located within total intensity map. The two solid black lines represent the I I H m IRAC Spitzer image. In each panel the black ellipse represe velocity field. Contours are separated by 15 km s µ I H 3.6 Top right panel: Bottom left panel: Position-velocity slices through the centre of NGC 2915 rev The position-velocity slices reveal another interesting f marking the systemic velocity at 465 km s velocity slices shown in Fig.width. 2. The open circle in the lower l Figure 1: Top left panel: Our changing view of the blue compact dwarf NGC 2915 of the old stellar disk and has semi-major and semi-minor axe 3.4 Non-circular motions gas motions (the slice positions and orientations are shown possible fast-rotating gas component manifests itselfhand as panel a of Fig.suggested 2. by The a galaxy large may fraction also of contain line a profiles central that exp are split b slice (right panel, Fig. 2). When this lagging gas is isolate leftpanel). Furthermore, line profilesNot near surprisingly, the these centre disturbed of H NG kpc) respectively. receding half of the galaxythe contains main a gas gas disk of component the that galaxy. is This gas c component appears as 2915 thereby placing them within thethus likely immediate that vicinity energy of from t star formation is disrupting th 3.5 Gas infall PoS(PRA2009)051 I α J. The H E. C. Elson 46 10 × line profiles in the 5 I ∼ beard and velocity spike total intensity map. The I I of NGC2915, being con- etre Array Project for generous e the H ing accreted from inter-galactic lar winds from the young stellar a highly dispersed, expanding gas total intensity map (Fig. 3). The as outwards, thereby emptying the es in the H I st of the anomalous features seen in . Such an energy output can account nished (Sancisi et al., 2008), fuelling ) and the velocity resolution is ved in nearby systems and is thought omponent to be 1 ral region as a rotating, expanding H ′′ l grant to attend the PRA meeting. All lent meeting. − lysis of NGC 2915 may therefore provide J s 5 . be (2.5 32 10 5 ∼ years, which is the typical main sequence lifetime 6 α 10 × 5 total intensity map. Since NGC 2915 is seemingly isolated, ∼ I over-densities seen in the H I emission also coincides with the observed split and broad H α feature seen in the H I . The white circle and ellipse in the right-hand panel enclos Position-velocity slices as represented by solid black lin 1 emission (Gil de Paz et al., 2003) is observed near the centre − α E. C. Elson would like to thank the South African Square Kilom H data products (Elson et al. in prep). I luminosity of NGC 2915 is measured to be H Figure 2: Our changing view of the blue compact dwarf NGC 2915 tained within the two central H central region of NGC 2915. Thiscomponent. may We estimate therefore the be energy evidence associated of with this gas c location of this H for the central gas energetics within 3.5 km s core dictate the inner gas dynamics ofinner NGC region 2915 of and the expel galaxy. the Results g torus from find modeling that of this the simple cent dynamicalH model can account for mo of a high mass O or B type star. We therefore argue that the stel respectively. plume-like H funding throughout the duration of this PhDauthors and wish for to the thank trave the conference organisers for an excel Acknowledgments thickness of the slices is that of a single pixel in the data cu conclusive evidence for the infall of pristine gas. 4. Central energetics such a gas component mayspace onto therefore NGC provide 2915. evidence Indeed, of gasto accretion be gas is the be mechanism directly by obser which astar galaxy’s formation gas in reservoir the is inner reple disk. A detailed metallicity ana PoS(PRA2009)051 contour I E. C. Elson over-density is at a level of I 9, AJ, 118, 2158 ne Data Catalog, 214, 70029 1996, AJ, 111, 1551 iety, 1351–+ ., & Makarov, D. I. 2004, AJ, 127, 2563 2 Bulletin of the American Astronomical T. 2008, A&A Rev., 15, 189 total intensity contours overlaid. H I 6 . The central-most contour of each H 2 − cm 20 10 × 5 . . The black ellipse is the same one shown in the moment maps. image from Gil de Paz et al. (2003) with H 2 − α H cm 21 10 × Society, Vol. 35, Bulletin of the American Astronomical Soc 2031 5 . levels are in steps of 1 Leroy, A. K., Walter, F., Brinks, E., et al. 2008,Masset, AJ, F. 136, S. 278 & Bureau, M. 2003, ApJ, 586, 152 Meurer, G. R., Carignan, C., Beaulieu, S. F., & Freeman,Meurer, K. G. C. R., Mackie, G., & Carignan, C. 1994,Sancisi, AJ, R., 107, Fraternali, 2021 F., Oosterloo, T., & van der Hulst, Steer, D. G., Dewdney, P. E., & Ito, M. R.van 1984, der A&A, Marel, 137, R. 159 P. & Franx, M. 1993, ApJ,Walter, F., 407, Brinks, 525 E., de Blok, W. J. G., et al. 2008, AJ, 136, Kennicutt, R. C., Bendo, G., Engelbracht, C., et al. 2003, in References Bureau, M., Freeman, K. C., Pfitzner, D. W., & Meurer, G. R. 199 Gil de Paz, A., Madore, B. F., & Pevunova, O.Karachentsev, 2003, I. VizieR Onli D., Karachentseva, V. E., Huchtmeier, W. K 1 Figure 3: Our changing view of the blue compact dwarf NGC 2915