Arbutina, B.

Pavlović, M.~Z.

Petrov, N.

Trčka, Ana

Urošević, D.

Vučetić, M.~M.

Ćiprijanović, A.

English

Ghent University Academic Bibliography

Astronomical and Astrophysical Transactions (AApTr), 2018, Vol. 30, Issue 4, pp. 379–386,ISSN 1055-6796, Photocopying permitted by license only, c©Cambridge Scientific PublishersOptical observations of NGC 1156 galaxy innarrowband [SII] and Hα filtersM.M. Vučetić1,†, A. Trčka1, B. Arbutina1, A. Ćiprijanović1, M.Z. Pavlović1,D. Urošević1, N. Petrov21Department of Astronomy, Faculty of Mathematics, University of Belgrade,Studentski trg 16, 11000 Belgrade, Serbia2National Astronomical Observatory Rozhen, Institute of Astronomy, BulgarianAcademy of Sciences, 72 Tsarigradsko Shosse Blvd, BG-1784 Sofia, BulgariaReceived 21 September, 2016We present observations of a Magellanic-type dwarf irregular galaxy NGC 1156 innarrow band [SII] and Hα filters, carried out in November 2015, with the 2 m RCCtelescope at Rozhen National Astronomical Observatory in Bulgaria. Although ourobservations were with the intention to find new extragalactic supernova remnant can-didates, we were successful in the detection of 59 HII regions. We give luminosityfunction and size distribution for the detected HII regions. Also, we found that re-lation between Hα luminosity and radius of HII regions in NGC 1156 has the slopeof 2.7 ± 0.2 in logarithmic presentation, which is in good agreement with theoreticalprediction for ionization-bounded HII regions.Keywords: Galaxies: individual: NGC1156–HII regions1 IntroductionNGC 1156 is a Magellanic-type dwarf irregular galaxy i.e. type IB(s)m, with apparentdimensions 3.3′ × 2.5′ in V band∗ at approximate distance of 7.6 Mpc (Kim et al.2012). The galaxy has a larger than average core and shows some signs of tidalinteractions, unusual for an isolated galaxy. The Arecibo Galaxy Environment Survey(AGES) finds a small dwarf galaxy AGES J030039+254656 about 35 arcmin north-east of NGC 1156. Although it seems unlikely that this dwarf galaxy, in its currentposition, could be exerting any significant tidal force on NGC 1156, the possibilityof an interaction in the past cannot be ruled out (Minchin et al. 2010). We havecarried out new optical observations of NGC 1156 in narrow band filters at NationalAstronomical Observatory (NAO) Rozhen in Bulgaria, with the intention of finding†Email: mandjelic@matf.bg.ac.rs∗From NED: http://ned.ipac.caltech.edu/380 VUČETIĆ ET AL.new supernova remnant candidates and HII regions in this galaxy. For supernovaremnants we expect [SII]/Hα emission line ratio higher than 0.4, while for HII regions[SII]/Hα ratio should be lower than 0.2 (e.g. Blair & Long 1997).2 Observations and data reductionObservations were carried out during two nights, November 3/4 - 4/5, 2015, with the2 m RCC telescope at NAO Rozhen. The telescope was equipped with VersArray:1300B CCD camera with 1340 × 1300 px array, plate scale of 0.25′′/px, giving the fieldof view 5′45′′ × 5′35′′. We took images through Hα, [SII] and red continuum filters,with total exposure time of 9600 s for each filter. Typical seeing was 1.5′′. Datareduction was done using standard procedures in IRIS†. For details see Arbutina etal. (2009), Andjelić et al. (2011), Vučetić et al. (2013, 2015).3 ResultsIn this paper we present the first optical survey of NGC 1156 galaxy for emissionnebulae. Although our observations were unsuccessful in detecting new extragalacticsupernova remnant candidates, we detected 59 HII regions. In order to classify de-tected objects, we made [SII]-0.4Hα image. Since all emission nebulae were dark inthis image, we concluded that there are no SNRs. Also, all sources were dark in [SII]-0.2Hα image, meaning that all HII regions have [SII]/Hα ratio less than 0.2. For thatreason we did not measure [SII] fluxes and in this paper omit continuum-subtracted[SII] image. Figure 1 represents observed region in Hα emission, with marked HII re-gions. The properties of the detected objects are listed in Table 1. We have measuredobjects’ Hα fluxes by subtracting sky from continuum-subtracted image, then settingimage median to zero and drawing 2σ contours around sources. To check Hα fluxes,we measured both contour and aperture fluxes – Fc, Fa, for several isolated objects.Although Fa are systematically larger then Fc, the difference is not very large and isprobably of the order of other uncertainties. If we define the flux quality measure asδ = 2|Fc − Fa|/(Fc + Fa), then δmax = 54%, while 〈δ〉 = 27%.In Fig. 2a we show the Hα luminosity function (LF) for detected HII regions inNGC 1156. HII regions LF is usually represented by a power law of the followingform: N(L)dL = ALadL. Kennicutt et al. (1989) found that the Hα LFs of brightHII regions in 30 nearby spiral and irregular galaxies are represented approximately bya power law with a = −2.0±0.5, with Magellanic type galaxies having shallowest LF.Our obtained LF for NGC 1156 HII has the slope of a = −1.0± 0.1 for luminositieslarger than logL [erg s−1] ≈ 38, where distribution’s maximum occurs. Maximum ofthe diameter distribution is around 100 pc (Fig. 2b). The angular resolution for oursample is ∼1.5′′ (seeing value), which corresponds to 60 pc.We examined the correlation between Hα luminosities and diameters of the de-tected objects. The slope of this correlation is an important diagnostic parameter ofconditions inside the HII region. According to the classical theory for the simple case†Available at http://www.astrosurf.com/buil/c©2018 Astronomical and Astrophysical Transactions (AApTr), Vol. 30, Issue 4OPTICAL OBSERVATIONS OF NGC 1156 GALAXY 381Figure 1 The continuum-subtracted Hα image of NGC 1156 galaxy. Numbers correspondto the entries in Table 1.of ionization-bounded HII region in constant density, Hα luminosity should scale thecube of the HII region diameter (Strömgren 1939, Osterbrock 1989). We found thatthe log–log plot of Hα luminosity versus R has the slope of b = 2.7 ± 0.2 (Fig. 2c),which is in good agreement with theory for ionization-bounded HII regions. Slopecoefficients found in the literature for different galaxies are in the range of 1.5–3, de-pending on the galaxy type and procedure used to derive the size of the HII region(e.g. Lee et al. 2011, Gutiérrez et al. 2011).4 SummaryIn this paper we presented the first optical survey of NGC 1156 galaxy for emissionnebulae, conducted from NAO Rozhen. We detected 59 HII regions, and no supernovaremnants. The relation between Hα luminosities and radii of detected HII regions inlog-log scale has the slope of 2.7, which is close to the theoretical prediction forionization-bounded HII regions.c©2018 Astronomical and Astrophysical Transactions (AApTr), Vol. 30, Issue 4382 VUČETIĆ ET AL.37.0 37.5 38.0 38.5 39.0 39.502468101214  (a)Number per 0.2 dexlog L [erg s-1]50 100 150 200 250 300 35005101520 (b)  Number per 30 pcD [pc]1.4 1.6 1.8 2.0 2.2 2.437.037.538.038.539.039.5log L = 2.7 log R + 32.9  (c)log L [erg s-1]log R [pc]Figure 2 (a) Hα luminosity function of HII regions in NGC 1156. Luminosities havebeen corrected for reddening (Schlafly & Finkbeiner 2011). (b) Diameter distribution. (c)Relation between the Hα luminosities and R in log-log scale.c©2018 Astronomical and Astrophysical Transactions (AApTr), Vol. 30, Issue 4OPTICAL OBSERVATIONS OF NGC 1156 GALAXY 383Table 1 Coordinates, angular diameters, mean radii and Hα fluxes for 59 detected objects.Adopted distance to the galaxy is 7.6 Mpc (Kim et al. 2012). Hα flux has not been correctedfor reddening.Source R.A. Dec. Angular diameter Radius Hα fluxNo. θ [arcsec] 〈R〉 [pc] F [10−15 erg s−1 cm−2]1 02:59:37.3 +25:14:28 3.6 × 3.6 70 14.32 02:59:40.5 +25:13:54 9.7 × 8.0 160 160.53 02:59:40.6 +25:14:28 2.7 × 2.7 50 3.84 02:59:40.8 +25:14:05 2.8 × 2.8 50 15.95 02:59:40.9 +25:14:07 3.1 × 1.8 40 10.46 02:59:40.9 +25:14:00 5.2 × 3.5 80 11.77 02:59:41.0 +25:13:56 6.2 × 4.9 100 25.58 02:59:41.2 +25:13:43 2.4 × 2.4 40 3.09 02:59:41.2 +25:13:50 7.0 × 7.2 130 63.510 02:59:41.5 +25:13:43 5.3 × 4.8 90 33.711 02:59:41.5 +25:13:56 7.0 × 7.3 130 66.612 02:59:41.6 +25:13:51 3.7 × 2.4 60 7.513 02:59:41.8 +25:14:32 4.9 × 3.2 80 13.814 02:59:41.8 +25:14:04 3.6 × 5.2 80 13.215 02:59:42.1 +25:13:48 3.0 × 5.3 80 33.816 02:59:42.1 +25:14:40 3.7 × 3.7 70 10.817 02:59:42.2 +25:14:13 2.2 × 2.8 50 22.618 02:59:42.2 +25:13:39 1.8 × 1.7 30 1.019 02:59:42.2 +25:13:50 4.9 × 1.7 60 9.920 02:59:42.3 +25:13:48 2.3 × 2.7 50 8.921 02:59:42.3 +25:13:57 3.0 × 3.1 60 4.522 02:59:42.3 +25:14:13 2.3 × 2.7 50 19.823 02:59:42.4 +25:14:51 4.0 × 2.8 60 6.824 02:59:42.7 +25:14:25 2.2 × 2.8 50 2.625 02:59:43.0 +25:14:21 2.3 × 2.4 40 2.726 02:59:43.0 +25:14:17 2.4 × 2.2 40 3.027 02:59:43.1 +25:14:03 2.6 × 1.7 40 1.428 02:59:43.2 +25:13:48 2.8 × 3.3 60 7.929 02:59:43.3 +25:15:20 3.6 × 3.7 70 2.130 02:59:43.3 +25:14:01 1.9 × 1.7 40 1.431 02:59:43.3 +25:14:33 4.4 × 3.1 70 10.432 02:59:43.3 +25:14:26 4.0 × 4.0 70 15.833 02:59:43.4 +25:14:38 3.5 × 3.0 60 6.734 02:59:43.4 +25:13:48 2.4 × 2.3 40 2.635 02:59:43.5 +25:14:50 6.1 × 4.9 100 44.336 02:59:44.1 +25:14:10 2.1 × 1.9 40 1.837 02:59:44.2 +25:14:03 3.5 × 4.8 80 18.938 02:59:44.3 +25:15:20 2.7 × 3.3 60 4.239 02:59:44.4 +25:14:02 4.3 × 2.5 60 12.140 02:59:44.5 +25:14:23 8.2 × 6.4 140 80.5Continued on next pagec©2018 Astronomical and Astrophysical Transactions (AApTr), Vol. 30, Issue 4384 VUČETIĆ ET AL.Table 1 (continued)Source R.A. Dec. Angular diameter Radius Hα fluxNo. θ [arcsec] R [pc] F [10−15 erg s−1 cm−2]41 02:59:44.5 +25:15:21 3.2 × 2.4 50 3.942 02:59:44.6 +25:14:00 2.8 × 4.5 70 15.743 02:59:44.8 +25:13:54 2.6 × 2.6 50 3.944 02:59:44.8 +25:14:25 4.4 × 5.0 90 13.845 02:59:44.9 +25:14:03 4.1 × 4.8 80 28.746 02:59:45.1 +25:15:11 4.8 × 4.3 80 10.747 02:59:45.3 +25:15:02 1.5 × 2.1 30 2.248 02:59:45.3 +25:14:10 1.9 × 1.9 40 1.449 02:59:45.4 +25:14:44 2.2 × 2.2 40 1.750 02:59:45.4 +25:15:02 2.2 × 2.1 40 4.851 02:59:45.5 +25:15:09 3.7 × 3.2 60 9.852 02:59:45.6 +25:15:03 2.4 × 2.2 40 3.453 02:59:45.7 +25:14:45 2.1 × 2.1 40 1.554 02:59:45.7 +25:15:11 4.3 × 3.1 70 9.655 02:59:45.7 +25:15:15 2.8 × 3.4 60 4.556 02:59:45.7 +25:14:59 4.5 × 3.9 80 30.057 02:59:45.9 +25:14:57 3.4 × 2.7 60 9.858 02:59:46.9 +25:15:01 3.0 × 2.6 50 4.159 02:59:48.8 +25:14:46 3.2 × 3.6 60 6.3Acknowledgements During the work on this paper the authors were financiallysupported by the Ministry of Education, Science and Technological Development ofthe Republic of Serbia through the projects No. 176004 and No. 176005. This workis a part of the joint project of Serbian Academy of Sciences and Arts and Bulgar-ian Academy of Sciences “Optical search for supernova remnants and HII regions innearby galaxies (M81 group and IC342)”. The authors gratefully acknowledge observ-ing grant support from the Institute of Astronomy and Rozhen National AstronomicalObservatory, Bulgarian Academy of Sciences.ReferencesAndjelić M. M., Stavrev K., Arbutina B., Ilić D., Urošević D., 2011, Baltic Astron.,20, 459Arbutina B., Ilić D., Stavrev K., Urošević D., Vukotić B., Onić D., 2009, Serb. Astron.J., 179, 87Blair W. P., Long K. S., 1997, ApJS, 108, 261Gutiérrez L., Beckman J. E., Buenrostro V., 2011, AJ, 141, 113Kennicutt R. C., Edgar B. K., Hodge P. W., 1989, ApJ, 337, 761Kim S. C., Park H. S., Kyeong J., Lee J. H., Ree C. H., Kim M. 2012, PASJ, 64, 23Lee J. H., Hwang N., Lee M. G., 2011, ApJ, 735, 75c©2018 Astronomical and Astrophysical Transactions (AApTr), Vol. 30, Issue 4OPTICAL OBSERVATIONS OF NGC 1156 GALAXY 385Minchin R. F., et al. 2010, AJ, 140, 1093Osterbrock D., 1989, Astrophysics of Gaseous Nebulae and Active Galactic Nuclei(Mill Valley, CA: Univ. Science Books)Schlafly E. F., Finkbeiner D. P., 2011, ApJ, 737, 103Strömgren B., 1939, ApJ, 89, 526Vučetić M. M., Arbutina B., Urošević D., Dobardžić A., Pavlović M. Z., Pannuti T.G., Petrov N., 2013, Serb. Astron. J., 187, 11Vučetić M. M., Ćiprijanović A., Pavlović M. Z., Pannuti T. G., Petrov N., Göker Ü.D., Ercan E. N., 2015, Serb. Astron. J., 191, 67c©2018 Astronomical and Astrophysical Transactions (AApTr), Vol. 30, Issue 4

Optical observations of NGC 1156 galaxy in narrowband [SII] and Hα filters

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Optical observations of NGC 1156 galaxy in narrowband [SII] and Hα filters

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