PoS(SSC2015)009 α , , d http://pos.sissa.it/ greement both with pre- velocity field of the same I persions. We investigate these oscopy Nearby Galaxy Survey érot data for the galaxy NGC 2280 Pérot interferometer on the Robert ere the difference between the H , olution H , Kristine Spekkens anada anations for their existence. tric data on several nearby spiral galax- abc ity versity of New Jersey ion f [email protected] , , T. B. Williams line of excited hydrogen. We have modeled these data with a ∗ e Commons α [email protected] , al License (CC BY-NC-ND 4.0). [email protected] , , J. A. Sellwood , & Rachel Kuzio de Naray a e ∗ modeling software and found these models to be in excellent a velocities is larger than would be expected from typical dis I DiskFit [email protected] We have obtained high-spatial-resolution spectrophotome Stobie Spectrograph (RSS) as a part of the RSS Imaging spectr ies with the Southern African Large Telescope (SALT) Fabry- (RINGS). We have successfully reduced two tracks of Fabry-P to produce a velocity field of the H Speaker. galaxy. Despite this good agreement, small regions exist wh and H the regions of high velocity difference and offer possible expl vious measurements in the literature and with our lower-res ∗ Copyright owned by the author(s) under the terms of the Creativ c K. Lee-Waddell Department of Physics and Astronomy, Rutgers, the State Uni Department of Physics, Royal Military CollegeP.O. Box of 17000, Canada Station Forces, Kingston, ON, K7K 7B4, XNS, C 136 Frelinghuysen Road, Piscataway, NJ 08854 Southern African Astronomical Observatory Observatory, Cape Town 7925, South Africa Astronomy Department, University of Cape Town Rondebosch 7700, South Africa SALT Science Conference 2015 1-5 June 2015 Stellenbosch Institute of Advanced Study, South Africa

Carl J. Mitchell The RINGS Survey: High-Resolution H-alpha Velocity Fields of Nearby Spiral GalaxiesSALT Fabry-Perot with the Attribution-NonCommercial-NoDerivatives 4.0 Internation 25 Park Place, Atlanta, GA 30303 E-mail: Commonwealth Scientific and Industrial Research Organisat Australia Telescope National Facility PO Box 76, Epping NSW 1710,Department Australia of Physics and Astronomy, Georgia State Univers [email protected] [email protected] f c e a b d PoS(SSC2015)009 and ′′ 011 in line of α calibrations, Carl J. Mitchell osing a single provide strong al gravitational ields a spectrum of-plane velocity ly as much of the for which we are ngest evidence for have performed an [8, 9]. Attempts at ximately 1.75 lations of bar flows tensity of the line is h of these nights, we lds of the H . These include pho- tion between bars and ver, it is not yet clear pix. line of excited hydrogen / i.e. higher concentrations tribution [1, 2, 3]. Galactic ′′ CDM cosmology. Precise α omparison. Λ Pérot observations of one of velocity map. lts. Mass models based on the- α 500 pc. CDM) has been very successful at Λ ∼ 4 pixel binning is 0.5 2 × 21 cm kinematic observations of this galaxy taken I is insufficient to provide such constraints, as the sep- ) R ( V ) spatial binning of the pixels in each individual Fabry-Pérot image. At ′′ 4.5 × ′′ 9 (4.5 kinematic observations of NGC 2280 were taken on 1 Nov 2011 and 28 Dec 2 × α Our H The left panel of Figure 1 shows the resulting line-of-sight H The circular speed of gas in a galaxy provides a direct estimate of the centr A one-dimensional rotation curve As a cosmological model, Lambda Cold Dark Matter ( Once the images are aligned and a wavelength solution has been found, cho In order to address this question, we have designed the RINGS program, The full details of our Fabry-Pérot data reduction are published in [16] , respectively. The scale of our images after 4 ′′ with the Karl G. Jansky Very Large Array (VLA) for the purposes of c 2. SALT Fabry-Pérot data excited hydrogen in 19 nearbythese galaxies. galaxies, NGC Here 2280. we present We also our present Fabry- H SALT Fabry-Perot H-alpha Velocity Fields 1. Introduction the distance to NGC 2280, this angular scale corresponds to explaining the origins ofwhether large-scale the structure small-scale in structure the of Universe galaxies [7]. can be Howe reproduced by measurements of the distribution of dark matterconstraints at for small cosmological radii models. within galaxies would pixel and measuring the imageat that intensity point. at that We have pixelstrong fitted across enough these all to spectra do of with so. our Voigtadditional profiles 9 images To wherever improve y the the in signal-to-noise ratio of these fits, we attraction in that galaxy, and therefore is arotation probe of curves that are galaxy’s mass known dis toextended halos flatten of at dark matter large [4, radii, 5, 6]. providing some of the stro using the Fabry-Pérot interferometer on SALT [15] to obtain 2D velocity fie 2 the medium-resolution mode of the SALTobtained Fabry-Pérot interferometer. 25 On one-minute eac exposures offrom the 6565.5 Å galaxy, to scanning 6643.5 over Å the in H 2 Å steps. The seeing on these nights was appro tometric calibrations with images fromnight-sky subtraction, the ghost CTIO subtraction, 0.9 and image m alignment. telescope [17], wavelength aration of dark and luminousresolving contributions this to degeneracy have the produced rotation significantly curveoretical different is arguments resu such degenerate as spiral-arm multiplicity [10,halos 11] [12] and favor dynamical maximal fric disk models,gravitational in force which as the is luminous permitted disk byhave provides the also near rotation favored curve. mass Hydrodynamical models simu dispersions with in maximal disk galaxies disks have been [13]. shownof to Measurements favor dark sub-maximal of matter disks, out- [14]. PoS(SSC2015)009 r Disk- axisym- associated r uncertainty (right) veloc- I Carl J. Mitchell , the systemic uch flexibility is After accounting f data-minus-model g model is 2.33, indi- antly improve the fits. (several effective beams tware is also capable of (left) and H kens/diskfit/ uncertainty. This suggests model in Figure 3. α data have higher spatial resolution DiskFit Residual maps to our best-fitting α data have a larger filling fraction and I models to our H Fit ity maps. Figure 2: 3 data. The H I software of [18] and [19] to fit idealized disk models to our velocity 21 cm aperture synthesis observations of NGC 2280 from the VLA. 1 I (right) velocity I DiskFit software fits a single tilted disk to the input velocity and uncertainty maps. The velocity map in the right panel of Figure 1. These data are complementary to ou (left) and H I α is publicly available for download at http://www.physics.rutgers.edu/~spek DiskFit Our H We have also obtained H We present the rotation curve derived from our best-fitting We have used the In modeling these data, we have added an additional 8 km/s in quadrature to ou DiskFit Fabry-Pérot data in numerous ways. For example, our H 1 α 4. Comparison to HI data map. The fitted parameters are the position of the center, the inclination, the position angle velocity, and the circular speedfitting at for any number asymmetries of such specifiedunnecessary as radii. for bars NGC The 2280; and such sof warps, non-axisymmetric models though do we not find signific thatmap allowing to account s for the turbulentfor motions this typical additional of the 8 interstellar km/s,cating medium the a [20]. poor reduced formal chi-squared fit valueresiduals to for for the our our best-fitting data. best-fittin model. The Thisacross) left residual of map panel correlated shows of large residuals regions Figure with magnitudes 2that larger shows than the a our kinematic map expected structure o ofmetric NGC model. 2280 For is example, more ourwith models complicated spiral do than arms. not is include permitted the by kinds our of streaming motions H 3. Kinematic models but lower spectral resolution than do our H fields of NGC 2280, presentedspatial scale. on Note the the same significant differences in spatial resolution, spatial extent,ing and fraction. fill- We present our H Figure 1: SALT Fabry-Perot H-alpha Velocity Fields PoS(SSC2015)009 I l e α < r 0 data R I < data in velocity I ′′ I kinematic data cube. I ions of large α Carl J. Mitchell meters for our and H ference between r, some spatially and H α error bars. In the e edges of the H 5 pixel binning of ections. In regions α × e strength is roughly model to our H models to the approaching l residual map for our best . The best-fitting systemic s between H DiskFit DiskFit Rotation curves produced from our DiskFit . ′′ 9 binned version of the same figure. Our 120 maps. Note that thecurve appears approaching to deviate (NW) from H the otherrotation three curves over the region 40 and receding sides of our H Figure 4: best-fitting × data with 9 spatial pixel binning in the H I × 4 ve- I and H α data appear to have a systematically higher circular speed than do data, except in the central region of the galaxy where the H α α are also produced by different phases of the ISM (excited and neutra I the H data, we have modeled our H ′′ and H Fabry-Pérot data and with previously published values in the literature (se α 120 α models to our H α velocity fields, shown in Figure 5. Most of the plotted pixels have values nea < model to these data. I r < Rotation curves produced from our DiskFit ′′ and H data. Figure 6 shows the resulting velocity difference map. Many of the reg data. DiskFit α α I Some of the regions of large velocity difference, in particular those near th As with our H We present the rotation curve derived from our best-fitting To further investigate this discrepancy, we have produced a map of the dif spatial extent than do the H the H km/s, demonstrating the close agreementcoherent between regions of the large two velocity difference sets exist. of Such data. difference Howeve measurements are not a new phenomenon [21, 22]. locity maps. exhibits a hole. H Figure 3. At mostregion radii, 40 the two rotation curves agree within their respective the H uniform, beam smearing has the effect of blurring velocities equally in all dir understanding of this phenomenon is as follows: in spatial regions where lin gas, respectively). Table 3 of [16]). The rightfitting panel of Figure 2 shows the data-minus-mode the H To investigate this, we have reproduced this velocity difference mapvelocity using difference are 5 less-pronounced than in the 9 velocity and geometric projectionmodels parameters agree of well the both H with the same para velocity map, may be a result of our choice of 9 best-fitting Figure 3: SALT Fabry-Perot H-alpha Velocity Fields PoS(SSC2015)009 I I d our and H 9 in pro- α × The profiles e profiles we Carl J. Mitchell fitted H profiles of several intensity areas, but ce in Figure 5. These ifferences. This effect over this area will blur e map. lain the systematic offset mation. velocities do not represent d to a region where the H . Furthermore, we have fitted α ′′ velocity map. Note that some of beam, indicating they are likely α 120 α Same as Figure 5, except that we have . We believe these features may be I < 5 pixel binning rather than 9 r × < ′′ Figure 6: used 5 the regions of large differencethe near map the have edges disappeared, of thoughremain. several areas ducing our H 5 intensity is not. The fitted H α velocity field and not the H α data cube and compared them to the line profiles of the corresponding I velocity maps at all I Fabry-Pérot data cube. For the vast majority of pixels, the two spectra an model rotation curves over the region 40 and H I α α Differences in line-of-sight velocity and H α These individual patches of large velocity difference alone do not exp To better understand these velocity differences, we have examined the line velocities differ significantly, taken fromregions a have region angular sizes of comparable high to velocity that differen of our effective H caused by some feature in the H evidence of bubbles or chimneys of excited gas in regions of high star for points where velocities wereboth measured lines. for Figure 5: between our H where line strength changes substantially overvelocities a preferentially small in area, a one beamnot direction placed the (from reverse). high-intensity The areasintensity edges to is of roughly lower- this uniform, but velocity the difference H map correspon SALT Fabry-Perot H-alpha Velocity Fields the true velocity at theseexplains some, pixels, but and certainly therefore not all, are of the the cause features of in the the velocity largeindividual differenc pixels d in our H fits to the line profile agreein quite the well. top We show panel twohave sample are examined line are typical profiles qualitatively in of similar. Figure pixels 7. The second in shows our a maps, pixel in and which most the of the individual lin pixels in our H in the H PoS(SSC2015)009 I in ) mod- ′′ DiskFit 75 − , ′′ endently. We ce in rotation DiskFit 0 Carl J. Mitchell , receding (SE) ificant effect on α les correspond to )=( it would correspond Figure 8. The peaks profiles from the re- al velocity in the H Y I , W) H spectrum (blue points), ve discrepancy is most our best-fitting X I ( am of neutral gas external to ) ′′ Two sample H 100 , ′′ 50 Figure 8: while the greenpredicted line from our denotes best-fitting the velocity gion of large positivepanel of residual Figure in 2. The the redted line right velocity shows of the the fit- H els to theskewness entire of velocity the profiles, map. withat a lower “shoulder” Note line-of-sight the pret velocity. this shoulder We as inter- galaxy’s rotation and corresponding the to peak as the gas a stream external of to the galaxy.shown are The from two spectra pixels separatedbeam-widths. by several )=( Y , X 6 ( I curve appears to be significantly different. I line profiles in this region and have found that many of them I curves all appear to be consistent with each other over the region of I (blue) data. Note the sig- I model circular velocity over this radial region, causing the large differen Two sample line profiles comparing models to the approaching and receding halves of the two velocity fields indep (red) and H α Here we note the presence of a large, spatially coherent, positive residu DiskFit , and receding (SE) H α the right panel of Figurepronounced. 2 We and have examined intersects the the H region where the rotation cur have a skewed shape or areof multiply peaked. these We profiles plot lie two such at line higher profiles recessional in velocities than are predicted by field. This region extends from approximately interest, while the approaching (NW) H model. We believe the lower-velocity “shoulders”the of galaxy’s rotation, these while asymmetric the line higher-velocity peak profi to corresponds the to galaxy. a Assuming stre this streamto of an gas is inflow in of the neutralthe foreground of gas. NGC 2280, We believe this stream of gas may be having a sign curves that we observe. spectrum. The profiles intypical the of top our panel data; are fitted the velocities two agree lines well. andthe bottom their The panel correspond spectra to a in pixel where the two maps do not agreeare well; rare such in pixels ourrescaled data. such that all Flux of the unitsvalue spectra of have peak 1. at been a H nificantly higher spectral resolution of the H Figure 7: our H SALT Fabry-Perot H-alpha Velocity Fields DiskFit show the resulting rotation curves in Figure 4. Note that the approaching (N PoS(SSC2015)009 ent ]. ApJ , (June, 440 y-Pérot 238 ion ]. 179 (Feb., 1977) ApJ Nature , , Carl J. Mitchell 54 A&A (1939) 41–51. , 19 igh spatial resolu- elocity fields pro- alaxies on smaller A&A . Our measurements , ]. at of NGC 2280. These (Sept., 1969) 859–876. astro-ph/0008205 (June, 1922) 406–410. 74 e galaxies NGC 5033, 3198, arXiv:1108.4314 55 AJ (July, 1997) 103–110, , C 2885 /R = 122 kpc/ ApJ 483 , neutral hydrogen in spiral galaxies of Distribution of dark matter in the spiral . B. Westfall, D. R. Andersen, and R. A. , ApJ , Lick Observatory Bulletin , astro-ph/0006275 (Oct., 2011) L47, [ (Jan., 2001) 931–951, [ ]. Halo parameters of spiral galaxies The Disk and Dark Halo Mass of the Barred Galaxy 7 velocity field in NGC 2280 agree very well with Rotational properties of 21 SC galaxies with a large 739 546 The large-scale structure of the Universe α ApJ ApJL , , (Dec., 1981) 1791–1846. Constraints from Dynamical Friction on the Dark Matter Cont Spiral instabilities provoked by accretion and star format 86 AJ (Nov., 2000) 704–721, [ A new method of determining distances to galaxies , (Aug., 1985) 305–313. astro-ph/0604561 543 ]. 295 ApJ ApJ , , The rotation of the Andromeda Nebula Integral Properties of Spiral and Irregular Galaxies Does the Milky Way Have a Maximal Disk? 21-cm line studies of spiral galaxies. I - Observations of th Galaxy Disks are Submaximal An estimate of the distance of the Andromeda Nebula. 21 cm observations and previous measurements in the literature. SALT Fabr I (July, 1984) 61–74. astro-ph/9608164 282 [ galaxy NGC 3198 5055, 2841, and 7331. II -various The morphological distribution types and kinematics of 1987) 23–40. of Barred Galaxies (June, 1980) 471–487. range of luminosities and radii, from NGC 4605 /R = 4kpc/ to UG 661–673. NGC 4123. II. 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Williams, data for 12 of theduced 19 from galaxies these in data in the many RINGShigh-resolution cases sample kinematic have are higher maps spatial are now resolutions allowing in than us hand,scales th to than and probe previously our the possible. v structure of these g References tion, we are measuring galaxyand velocity fields subsequent on kinematic previously modeling unmatched of scales the H [14] M. A. Bershady, T. P. K. Martinsson, M. A. W. Verheijen, K both our H SALT Fabry-Perot H-alpha Velocity Fields 5. Summary PoS(SSC2015)009 , n to es Carl J. Mitchell (May, 2008) 135 (Mar., 2015) 116, AJ , in prep. , ]. 149 Modeling the Gas Flow in the AJ , ]. An Imaging System FABRY-PÉROT ]. arge Telescope Williams, ell, R. Kuzio de Naray, and J. A. Sellwood, Joseph, (Aug., 1979) 1181–1188. 84 arXiv:0710.5286 AJ , 8 The global properties of the Galaxy. II - The Galactic NGC 4254: A Spiral Galaxy with an M = 1 Mode and astro-ph/0703688 arXiv:0912.5493 ]. 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