HI observations of nearby galaxies - I. The first list of the Karachentsev catalog

Astronomy and Astrophysics Supplement Series, Jul 2018

We present HI observations of the galaxies in the first list of the Karachentsev catalog of previously unknown nearby dwarf galaxies (Karachentseva & Karachentsev 1998). This survey covers all known nearby galaxy groups within the Local Volume (i.e. within 10 Mpc) and their environment, that is about 25% of the total sky. A total of 257 galaxies have been observed with a detection rate of 60%. We searched a frequency band corresponding to heliocentric radial velocities from -470 km s-1 to ~+4000 km s-1. Non-detections are either due to limited coverage in radial velocity, confusion with Local HI (mainly in the velocity range -140 km s-1 to +20 km s-1), or lack of sensitivity for very weak emission. 25% of the detected galaxies are located within the Local Volume. Those galaxies are dwarf galaxies judged by their optical linear diameter (1.4 ± 0.2 kpc on the average), their mean total HI mass (4.6 107 ), and their observed linewidths (39 km s-1).

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HI observations of nearby galaxies - I. The first list of the Karachentsev catalog

Astron. Astrophys. Suppl. Ser. HI observations of nearby galaxies I. The 2 W.K. Huchtmeier 2 3 I.D. Karachentsev 1 2 V.E. Karachentseva 0 2 M. Ehle 2 4 0 Astronomical Observatory of Kiev University , Kiev , Ukraine 1 Special Astrophysical Observatory, Russian Academy of Sciences , N. Arkhyz, KChR, 357147 , Russia 2 Send o print requests to: W.K. Huchtmeier 3 Max-Planck-Institut fu ̈r Radioastronomie , Auf dem Hu ̈gel 69, D-53121 Bonn , Germany 4 Max-Planck-Institut fu ̈r Extraterrestrische Physik, Giessenbachstra e , D-85740 Garching bei Mu ̈nchen , Germany We present HI observations of the galaxies of 10 Mpc) increased to 303 objects (Karachentsev et al. in the rst list of the Karachentsev catalog of previ- 1999). For the past decade the initial KKT sample has ously unknown nearby dwarf galaxies (Karachentseva & been increased almost two times in number due to the Karachentsev 1998). This survey covers all known nearby mass redshift surveys of galaxies from the known catagalaxy groups within the Local Volume (i.e. within logues, revealing new nearby galaxies in the Milky Way 10 Mpc) and their environment, that is about 25% of \Zone of Avoidance", as well as special searches for dwarf the total sky. A total of 257 galaxies have been observed galaxies in nearby groups. The increasing numbers of with a detection rate of 60%. We searched a frequency galaxies in the Local Volume is mainly due to many new band corresponding to heliocentric radial velocities from dwarf galaxies. This fact demonstrates how incomplete −470 km s−1 to +4000 km s−1. Non-detections are our knowledge about the galaxy population of even the either due to limited coverage in radial velocity, confusion Local Volume is. with Local HI (mainly in the velocity range −140 km s−1 A couple of years ago Karachentseva & Karachentsev to +20 km s−1), or lack of sensitivity for very weak (1998; hereafter KK98) initiated an all-sky search for canemission. 25% of the detected galaxies are located within didates for new nearby dwarf galaxies using the second the Local Volume. Those galaxies are dwarf galaxies Palomar Sky Survey and the ESO/SERC plates of the judged by their optical linear diameter (1.4 0.2 kpc on southern sky. The results of the rst two segments of the the average), their mean total HI mass (4.6 107 M ), and survey have been published, they cover large areas around their observed linewidths (39 km s−1). the known galaxy groups in the Local Volume (KK98) and the area of the Local Void (Karachentseva et al. 1999). In - The only way to study the smallest galaxies is to search for them in our cosmic neighborhood. The rst systematic catalog of nearby galaxies was prepared by Kraan-Korteweg & Tammann (1979) who collected all known galaxies with corrected radial velocities v0 500 km s−1, a total of 179 objects (hereafter called the KKT sample). Since that time the number of known galaxies within the Local Volume (i.e. within a distance 2. Observations Observations were performed with three di erent radio telescopes for di erent declination ranges. The 100-m radiotelescope at E elsberg was used for declinations greater 0.0 800.0 0.0 0.060 0.030 0.000 -0.030 0.100 0.050 0.000 kk152 N4523 3200.0 800.0 800.0 800.0 800.0 1600.0 800.0 1600.0 800.0 1600.0 1600.0 kk233 kk238 800.0 1600.0 800.0 1600.0 0.0 800.0 0.0 800.0 1600.0 Fig. 2. HI pro les observed with the Nancay radio telescope (HPBW of 3:06 220 for the declination range in question) than −31 , the Nancay radio telescope was selected for galaxies in the declination range −38 −31 , and the compact array of the Australia Telescope was used for galaxies south of −38 . 2.1. E elsberg observations The radio telescope at E elsberg has been used in the total power mode (ON { OFF) combining a reference eld 5 min earlier in R.A. with the on-source position. A dual channel HEMT receiver had a system noise of 30 K. The 1024 channel autocorrelator was split into 4 bands (bandwidth 6.25 MHz) of 256 channels each shifted in frequency by 5 MHz with respect to their neighbor in order to cover a velocity range from −470 to 3970 km s−1 overlapping 1.5 MHz between channels. The resulting channel separation was 5.1 km s−1 yielding a resolution of 6.2 km s−1 (10.2 km s−1 after Hanning smoothing). The HI pro les observed with the 100-m radiotelescope are presented in Fig. 1 in order of increasing R.A. as in Table 1. The half power beam widths (HPBW) of the E elsberg telescope at this wavelength is 9:03. 2.2. Nancay observations For 15 galaxies in the declination range −38 −31 the Nancay radio telescope was used with the same velocity resolution and coverage. Major di erences to the description given for the E elsberg observations were a di erent system noise (45 K), a di erent antenna beam (3:06 220 in R.A. and Dec. for this declination range), and shorter integration phases with a cycle of 2 minutes for the ON and the OFF positions. Nine galaxies have been detected (Fig. 2). 2.3. Compact Array of the Australia Telescope 40 of the 57 galaxies south of declination −38 have been observed with the Compact Array of the Australia Telescope. For this HI search we have chosen the 750A antenna array con guration in order to yield an antenna beam comparable to the optical size of the smallest galaxies (i.e. 10). The frequency setup and correlator con guration was such that we obtained a velocity coverage from −450 to +2900 km s−1 and a channel separation of 6.6 km s−1 (i.e. a resolution of 7.9 km s−1). Each galaxy was observed for 10 min every few hours. With ve to six observations per target position we achieved a regular coverage of the uv plane for these \snapshot mode" observations. The resulting integrated HI pro les are given in Fig. 3 (for a more detailed discussion of these data see Huchtmeier et al. in preparation). We may miss some flux with the interferometer (missing flux) as the observed HI emission extends over more than 20 per channel for over 60% of the galaxies. Galaxies from the kk98 sample not observed are: kk 11, kk 63, kk179, kk 184, kk 189, kk 190, kk 197, kk 203, kk 211, kk 213, kk 214, kk 217, kk 221, kk 222, kk 235, kk 244, kk 248. 3. The data Our search list was an early version of the list of KK98 containing a few additional galaxies which did not make it into the nal version because of their morphology and/or size (i.e. they were too small). Particularly, we took into account the results of HI searches for nearby dwarf galaxies made by Kraan-Korteweg et al. (1994) , Huchtmeier et al. (1995) , Burton et al. (1996) , Huchtmeier & van Driel (1996), Huchtmeier et al. (1997) and Cote et al. (1997) . The optical data of our galaxies are given in Table 1. The kk-number (or other identi cation if there is no kknumber) is given in Col. 1, R.A. and Dec. (1950) follow in Cols. 2 and 3. The optical diameters a and b in the de Vaucouleurs (D25) system follow in Cols. 4 and 5, the morphological type in Col. 6 where we use the following coding: Im - irregular blue object with bright knot(s); Ir - irregular without knots or with amorphous condensations, the colour is neutral or bluish; Fig. 3. HI pro les observed with the Australia Telescope Compact Array. The synthesized antenna beam is of the order of 10 Sm - disturbed spiral or irregular with signs of spiral structure; Sph - spheroidal, with very low brightness gradient or without any, the color is neutral or redish. The optical surface brightness (SB) has been coded (see KK98): high (H), low (L), very low (VL), and extremely low (EL) in Col. 7. The total blue magnitude Bt and its reference follow in Cols. 8 and 9. \NED" - data are from the NASA/Extragalactic Database, \IK" - visual estimates from POSS (typical error is about 0.4 mag) by I. Karachentsev, \6 m" - accurate photometric data from the 6-m telescope CCD-frames obtained by Karachentsev and coworkers (unpublished); \UH" - photometric data from U. Hopp (Calar Alto) unpublished. The Galactic extinction follows in Col. 10. Other names (identi cations) are listed in Col. 11. Results of the HI observations are summarized in Table 2. The kk-number is given in Col. 1, the HI-flux [Jy km s−1] follows in Col. 2, the maximum emission and/or the rms noise [mJy] in Col. 3, the heliocentric radial velocity plus error in Col. 4, the line widths at the 50%, the 25%, and the 20% level of the peak emission in Col. 5. Distances (Col. 6) have been derived with di erent methods, there are photometric distances in some cases, in other cases the group membership yields a distance. If no other distance estimate is available, we assumed a Hubble constant of 75 km s−1 Mpc−1 to derive a \kinematic" distance. The absolute magnitude is given in Col. 7, the integrated HI mass (Col. 8) was calculated as (e.g. Roberts 1969) (MHI=M ) = 2:355 105 D2 Z Svdv where D is the distance of the galaxy in Mpc and R Svdv is the integrated HI flux in Jy km s−1. The relative HI content MHI=LB follows in Col. 9. Finally, Col. 10 contains comments relative to the telescope used for the observation: unless otherwise noted observations have been performed with the 100-m radiotelescope at E elsberg, N marks the Nancay radio telescope, ATCA - the Australia Telescope Compact Array at Culgoora, NSW. In a number of cases emission at negative radial velocities has been observed (kk 20, kk 236, kk 237; only kk 236 has been plotted as an example). The Dwingeloo HI survey (Hartmann & Burton 1997) has been consulted: in all cases of negative radial velocities extended HI emission was found suggesting that we observed high velocity clouds in our Galaxy. 4. Discussion A great majority (73%) of our galaxies are of type Im (26) and Ir (162), about 20% are of type Sph/Ir (12) and Sph (39), while the rest of 8% is a collection of di erent types from spiral to Im/Sm and BCD. The detection rate of our sample galaxies depends on the morphological type. Fig. 5. The distribution of the optical linear diameter A0 in kpc for the whole sample in the de Vaucouleurs (D25) system is given here. Galaxies within 10 Mpc (i.e. within the Local Volume) are shown by shaded areas. The medium value for the shaded areas is 1:4 0:2 kpc 75% of the spirals (type S0 to Sm/Im and BCD) were detected; the detection rate for types Im and Ir is very similar close to 60%, whereas the detection rate for types Sph/Ir and Sph is considerable lower at 33 and 23%, respectively. The detection rate depends on the optical surface brightness (SB) class, too. From high SB to low, very low, and extremely low SB the detection rate decreases from 70% to 58%, 49%, and 43%, respectively. This trend reflects the type dependence and the fact that we deal with fainter galaxies as we descend from high SB to very low SB, the median absolute magnitudes for the detected galaxies change from −15:43 (H) to −13:92 (VL) for our brightness classes. A number of the galaxies within the present sample are associated with nearby groups of galaxies (e.g. Tully 1988) according to their position, radial velocity and relative resolution: NGC 672 group: kk 13, kk 14, kk 15; NGC 784 group: kk 16, kk 17; Ma ei group: kk 19, kk 21, kk 22, kk 23, kk35 kk 44; Orion group: kk 49; M 81 group: kk 81, kk 83, kk 85, kk 89, kk 89, kk 91; Leo group: kk 94; CVn cloud: kk 109, UGC 7298, kk 137, kk 141, kk 144, kk 148, kk 149, kk 151, kk 154, kk 158, kk 160, kk 191, kk 206, kk 220, kk 230; Centaurus group: kk 170, kk 179, kk 182, kk 190, kk 191, kk 195, kk 197, kk 200, kk 211, kk 217, kk 218; NGC 6946 group: kk 250, kk 251, kk 252; There are a few cases of high MHI=LB values in Table 2. Four of the ve galaxies with MHI=LB 5 are actually found to be confused by emission from nearby galaxies (see footnotes to Table 2). The present sample of galaxies as presented in Tables 1 and 2 will be discussed now in some detail with the help of global parameters. The distribution of radial velocity (v0, corrected for the rotation of our galaxy) is given in Fig. 4. Apart from a few background objects most of the galaxies belong to the local supercluster, about 25% are within the Local Volume. From this situation it is clear that the great majority of the galaxies in the present sample are dwar sh in nature. This will be shown more convincingly below when we compare several other global parameters of these objects. Next we will look at the optical linear diameter A0 (in kpc). The histogram in Fig. 5 presents the number of galaxies binned in intervals of 0.5 kpc width. The distribution of the optical linear diameters of our galaxies extends from 0.2 kpc to 26 kpc, yet the great majority is smaller than 8 kpc in diameter (in the de Vaucouleurs D25 system). Galaxies in the Local Volume (indicated by shaded areas) are even smaller with a median value of 1.4 0.2 kpc. Now we will use the correlation of two global parameters to compare the present sample of galaxies with the previously known galaxies in the Local Volume. In Fig. 6 the total mass of neutral hydrogen MHI of the galaxies is plotted versus their linear extent A0 for this sample of galaxies. The full line is the regression line for the KKT sample (Huchtmeier & Richter 1988) . This regression line seems to be an excellent t for the present sample, too. Fig. 7. The distribution of line widths of our galaxy sample is given for the observed values (dv) in the upper panel and for the (for inclination corrected values (dvi) in the lower panel. Galaxies within the Local Volume (i.e. within 10 Mpc) are marked by the shaded areas The average HI mass of the galaxies in the Local Volume is 4.6 107 M . The HI masses in Fig. 6 cover a range from 106 to 1010 solar masses. The HI luminosity function for galaxies has been studied with galaxies of 107 and more solar masses in HI so far. With the data of the new dwarf galaxies within the Local Volume we will be able in the end to discuss the HI luminosity function starting from 106 solar masses. The galaxies in our sample have small line widths on the average. In Fig. 7 we present the distribution of observed line widths in the upper panel and the (for inclination) corrected line widths in the lower panel. The optical axial ratio has been used here to derive the inclination. Galaxies within the Local Volume are indicated by the shaded areas. The peak of the line width distribution of the galaxies within the Local Volume is 39 km s−1 for the uncorrected and 47 km s−1 for the corrected line widths. The three global parameters we have considered so far point altogether toward the dwar sh character of the Local Volume objects in our sample: the average linear diameter of 1:4 0:2 kpc (Fig. 5), the mean total HI mass of 4.6 107 M and the small line width of less than 50 km s−1. Two more global parameters are shown in Fig. 8, pseudo HI surface density HI and the relative HI content MHI=MT. The pseudo HI surface density is obtained by dividing the total HI mass MHI of the galaxy by the disk area of the galaxy as de ned by its optical diameter A0. This quantity is given in units of solar mass per square parsec as well as in the usual HI column density NHI in atoms cm−2. This quantity is plotted versus the relative HI content MHI=MT. Our galaxies ll the usual range in HI surface density as well as in relative HI content as observed for normal galaxies (e.g. HR). The present sample of galaxies is relatively rich in HI. Some of the scatter in the diagram is due to uncertainties in observed quantities, the local HI emission (i.e. within −140 to +20 km s−1) and especially the inclination which is used to correct the line for 20% of HI-poor (spheroidal and Sph/Ir) objects in the width which itself enters the total mass calculation by the sample. Most of the detected galaxies are located within square. The optical diameters are uncertain for galaxies the local supercluster, and about 25% are members of the at low galactic latitudes due to the high foreground Local Volume. The dwarfs within the Local Volume have extinction, e.g. Cas 2, ESO 137{G27, BK12, ESO 558{11. a mean linear diameter of 1:4 0:2 kpc, a mean observed If we exclude the confused galaxies and those with linewidths of 39 km s−1, and a mean total HI mass of 4.6 heavy galactic extinction all entries in Fig. 8 with HI 107 M . The smallest galaxies have HI masses of just over 100 M pc−2 are gone. Low values of the HI surface den- 106 solar masses. Once this full-sky survey will be nished sity are not only due to the uncertainties of observational we will be able to discuss the luminosity function of the data, the gas content of dwarf galaxies is very sensitive to Local Volume including these tiny dwarf galaxies. This inoutside influences (tidal interactions) due to their shallow vestigation is especially needed as recent determinations gravitational potential. of the galaxy luminosity function exhibit an increase for Finally we plot the HI surface brightness versus the low mass objects. The exact value of this increase will optical surface brightness (Fig. 9). The surface brightness be important for deriving the mass density in the local class (Table 1, Col. 7) has been coded from 4 to 1 from universe. high SB to extremely low SB in steps of 1. The di erent errors of the mean values of each class essentially depend Acknowledgements. The Australia Telescope is funded by on the di erent population size of each SB class. However, tFhaecilCitoymmmaonnawgeeadltbhy oCfSAIRuOst.ralia for operation as a National there is a de nite trend of the HI surface density to grow with increasing optical SB by a factor of 2 to 4 (e.g. van der Hulst et al. 1993; de Blok 1997) . 5. Conclusion In this paper we presented an HI search for 257 candidates for nearby dwarf galaxies. A detection rate of 60% on the average is quite high keeping in mind the limited velocity band and the fact that single-dish telescopes are literally \blind" for weak emission in the velocity range of The Nancay Radio Astronomy Observatory is the Unite Scienti que de Nancay of the Observatoire de Paris, associ ated as Unite de Service et de Recherche (USR) No. B704 to the French Centre National de la Recherche Scienti que (CNRS). The Observatory also gratefully acknowledges the nancial support of the Conseil Regional of the Region Centre in France. This research has made use of the NASA/IPAC Extragalactic Database (NED) which is operated by the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration. This work has been partially supported by the Deutsche Forschungsgemeinschaft (DFG) under project No. 436 RUS 113/470/0 and Eh 154/1-1. 7 Bt 8 KK 1 IK IK NED NED NED 6m IK IK IK IK Ab 10 IK kk 4: heliocentric velocity = 1651 km s−1 (NED) kk 7, 9, 10: undetected in HI (2) kk 8, 12, 5: ANDI, II, III have been searched for HI within the radial velocity range −550 to 770 km s−1 kk 18, 26, 32: undetected in HI (3) kk 20: probably local HI kk 35: resolved, companion to IC 342 kk 42: undetected in HI (3) kk 61: undetected in HI (6), companion of NGC 2403 kk 65: companion of UGC 3974 kk 68: v = 738 km s−1 (1) kk 69, 70: companion of NGC 2683 kk 71: local HI? kk 74: undetected in HI (5) kk 78: UGC 5272B, confusion with UGC 5272 at 1.90 ATCA N N kk 82: 150 from PGC 29086 (v = 662 km s−1) kk 84: companion of NGC 3115 kk 87: heliocentric velocity 969 km s−1 (NED) kk 88: heliocentric velocity 263 and 2982 km s−1 (6) kk 89: highly probably member of M 81 group, HI emission probably not from this object kk 94, 96: near Leo triplet kk 103: heliocentric velocity 1894 km s−1 (NED) kk 108: NGC 3782 (v = 739 km s−1) at 7.60 NW, de nitely confused in HI kk 127: in spite of v = 131 km s−1 the galaxy looks distant kk 129: undetected in HI (7) kk 138: NGC 4295 (v = 8568 km s−1) at 40, no confusing object to be seem kk 146: heliocentric velocity 162 km s−1 (6) kk 150: heliocentric velocity 468 km s−1 (6) kk 155: heliocentric velocity 61 km s−1 (6) kk 162: the object looks like an emulsion defect kk 164: v = 4660 km s−1 (NED), NGC 4688 (v = 987 km s−1) at 6.70 SW: confused kk 170: HI detection by Matthewson & Gallagher (1995 ) kk 174: v = 1905 km s−1 conflicts with the galaxy morphology kk 177, 180: undetected in HI (7) kk 191: NGC 5055 (v = 510 km s−1, W = 406 km s−1) at 24.10 E, possible confusion through far sidelobe kk 192: NGC 5033 (v = 876 km s−1, W = 452 km s−1) at 10.80 W, di erent velocity range, no confusion kk 205: undetected in HI (6) kk 208: 200 from NGC 5236, confusion with the extended HI-halo of M 83 (4) KK HI-flux No. Jy km s−1 1 2 12.32 2.03 2.17 18.8 20.0 14.62 1.36 33 53 25 13.2 9.1 11.0 MBt 3.17 20.15 0.78 10 ATCA ATCA N ATCA ATCA Burton W.B. , Verheijen E.B. , Kraan-Korteweg R .C., Henning P.A. , 1996 , A &A 293 , L33 Cote S. , Freeman K.C. , Carignan C. , Quinn P.J. , 1997 , AJ 114 , 1313 de Blok W.J.G. , 1997 , Ph.D. Thesis, University of Groningen Gallagher J.S., Littleton J.E. , Mathews L.D. , 1995 , AJ 109, 2003 Hartmann D. , Burton W.B. , 1997 , Atlas of Galactic Neutral Hydrogen. 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Nachr. 300 , 181 (KKT) Kraan-Korteweg R .C., Loan A.J. , Burton W.B. , et al., 1994 , Nat 372 , 77 Matthews L.D. , Gallagher J.S. , Littleton J.E. , 1995 , AJ 110 , 581 Paturel G. , Fouque P. , Bottinelli L. , Gouguenheim L. , 1992 , Catalogue of Principal Galaxies, Lyon (PGC) Roberts M.S. , 1969 , AJ 74 , 859 Schombert J.M. , Bothun G.D. , Schneider S.E. , McGaugh S.S. , 1992 , AJ 103 , 1107 Tully R.B ., 1988 , Nearby Galaxy Catalog. Cambridge Univ. Press

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W. K. Huchtmeier, I. D. Karachentsev, V. E. Karachentseva, M. Ehle. HI observations of nearby galaxies - I. The first list of the Karachentsev catalog, Astronomy and Astrophysics Supplement Series, 469-490, DOI: 10.1051/aas:2000324