TheDraco Dwarf is aspheroidal galaxy which was discovered byAlbert George Wilson ofLowell Observatory in 1954 on photographic plates of theNational Geographic Society'sPalomar Observatory Sky Survey (POSS).[6] It is part of theLocal Group and asatellite galaxy of theMilky Way galaxy. The Draco Dwarf is situated in the direction of theDracoConstellation at 34.6°[7] above thegalactic plane.
| Draco Dwarf | |
|---|---|
.jpg) Field image of the Draco dwarf spheroidal galaxy, by theDigitized Sky Survey | |
| Observation data (J2000epoch) | |
| Constellation | Draco |
| Right ascension | 17h 20m 12.4s[1] |
| Declination | +57° 54′ 55″[1] |
| Redshift | −292 ± 21 km/s[1] |
| Distance | 260 ± 30kly (75.4kpc)[2][3][4] |
| Apparent magnitude (V) | 10.9[1] |
| Characteristics | |
| Type | E pec[1] |
| Mass | 1.2×108[4][e] M☉ |
| Apparent size (V) | 35.5′ × 24.5′[1] |
| Notable features | Highest known dark matter concentrated object |
| Other designations | |
| Draco Dwarf Spheroidal,[1] Draco dSph,[5]UGC 10822,[1]PGC 60095,[1]DDO 208,[1] | |
Characteristics
editPaul W. Hodge analyzed the distribution of its stars in 1964 and concluded that itsellipticity was 0.29 ± 0.04.[7] Recent studies have indicated that the galaxy may potentially hold large amounts ofdark matter.[8] Having an absolute magnitude of −8.6[c] and a total luminosity of only 2×105 L☉, it is one of the faintest companions to our Milky Way.[5]
Draco Dwarf contains manyred giant branch (RGB) stars; fivecarbon stars have been identified in Draco Dwarf and four likelyasymptotic giant branch (AGB) stars have been detected.[5]
The Draco Dwarf is estimated to be 80 ± 10 kpc[2][3] fromEarth and span a distance of 830 ± 100 × 570 ± 70 pc.[d]
RR Lyrae
editIn 1961,Walter Baade andHenrietta H. Swope studied Draco Dwarf and discovered over 260variables, of the 138 in the cluster's center, all but five were determined to beRR Lyrae variables.[9] From this work a RR Lyrae deriveddistance modulus of 19.55[a] is found which implies a distance of 81 kpc.[b]
Metallicity
editThe Draco Dwarf contains primarily anold population of stars and insignificant amounts ofinterstellar matter (being basically dust free).[5] From 75% to 90% of its stars formed more than ~10 Gyr ago followed by a low rate of formation with a small burst of star formation around 2–3 Gyr ago.[10] It has a singleGaussian distribution with average metallicity of [Fe/H] = −1.74 dex with astandard deviation (sigma/σ) of 0.24 dex and a small tail of metal-rich stars.[5] The central region of Draco Dwarf exhibits a concentration of more metal-rich stars there being more centrally concentrated redhorizontal branch stars than blue horizontal branch stars.[5]
Dark matter
editRecently, dwarf spheroidal galaxies have become key objects for the study ofdark matter. The Draco Dwarf is one which has received specific attention.Radial velocity computations of Draco have revealed a large internal velocity dispersion giving a mass to luminosity ratio of up to 440 M☉/L☉, suggesting large amounts of dark matter. It has been hypothesized that large velocity dispersions could be explained astidal dwarfs (virtually unbound stellar streams from dwarf galaxies tidally disrupted in the Milky Way potential). However, Draco Dwarf's narrowhorizontal branch width does not support this model.[11] This only leaves the dark matter explanation and makes Draco Dwarf the most dark matter dominated object known as of 2007.[5] The dark matter distribution within Draco Dwarf is at least nearlyisothermal.[8]
At large radii, radial velocity dispersion exhibit strange behavior. One possible explanation for this would be the presence of more than one stellar population. This suggests the need for further study of Draco Dwarf population's metallicity and ages and of dwarf spheroidals in general.[5]
In 2024, a group of scientists using theHubble Space Telescope measuredproper motions of Draco with 18 years of data, making it the firstdwarf galaxy to have its 3D velocity dispersion profile radially resolved.[4] The group of astronomers showed that Draco'sdark matter distribution is in better agreement with theLCDM model, helping to alleviate thecusp-core problem.[12]
Notes
edit- ^ Assuming an absolute magnitude of +0.5 V for RR Lyrae the apparent modulus of the Draco Dwarf is 19.58 m−M.[7] Using a reddening value towards Draco Dwarf of 0.03 ± 0.01[5] we get a true distance modulus of 19.55.
- ^ Using the distance modulus formula of 1×10(0.2 * 19.55 + 1) we get an RR Lyrae estimated distance of 81 kpc.
- ^ Apparent Magnitude of 10.9[1] – distance modulus of 19.52 (80 kpc) = −8.6
- ^ distance 80 ± 10 kpc × tan(diameter_angle = 35.5′ × 24.5′[1]) = 830 ± 100 × 570 ± 70 pc diameter
- ^ The quoted total mass is the cumulative dark matter mass (much higher than the luminous mass) at 900 pc from the galaxy's center.
References
edit- ^abcdefghijkl"NASA/IPAC Extragalactic Database".Results for Draco Dwarf. Retrieved2008-04-08.
- ^abI. D. Karachentsev; V. E. Karachentseva; W. K. Hutchmeier; D. I. Makarov (2004), "A Catalog of Neighboring Galaxies",Astronomical Journal,127 (4):2031–2068,Bibcode:2004AJ....127.2031K,doi:10.1086/382905.
- ^abKarachentsev, I. D.; Kashibadze, O. G. (2006), "Masses of the local group and of the M81 group estimated from distortions in the local velocity field",Astrophysics,49 (1):3–18,Bibcode:2006Ap.....49....3K,doi:10.1007/s10511-006-0002-6,S2CID 120973010.
- ^abcVitral, E.; et al. (2024)."HSTPROMO Internal Proper-motion Kinematics of Dwarf Spheroidal Galaxies. I. Velocity Anisotropy and Dark Matter Cusp Slope of Draco".The Astrophysical Journal.970 (1): 1.arXiv:2407.07769.Bibcode:2024ApJ...970....1V.doi:10.3847/1538-4357/ad571c.
- ^abcdefghiFaria, D.;Feltzing, S.; Lundström, I.; Gilmore, G.; Wahlgren, G. M.; Ardeberg, A.; Linde, P. (April 2, 2007), "The usage of Strömgren photometry in studies of local group dwarf spheroidal galaxies. Application to Draco: a new catalogue of Draco members and a study of the metallicity distribution function and radial gradients",Astronomy and Astrophysics,465 (2):357–373,arXiv:astro-ph/0611883,Bibcode:2007A&A...465..357F,doi:10.1051/0004-6361:20065244,S2CID 55281148
- ^Wilson, Albert George (February 1955), "Sculptor-Type Systems in the Local Group of Galaxies",Publications of the Astronomical Society of the Pacific,67 (394):27–29,Bibcode:1955PASP...67...27W,doi:10.1086/126754
- ^abcHodge, Paul W. (December 1964), "Distribution of stars in the Draco dwarf galaxy",The Astronomical Journal,69: 853,Bibcode:1964AJ.....69..853H,doi:10.1086/109360
- ^abTyler, Craig (July 2002), "Particle dark matter constraints from the Draco dwarf galaxy",Physical Review D,66 (2): 023509,arXiv:astro-ph/0203242,Bibcode:2002PhRvD..66b3509T,doi:10.1103/PhysRevD.66.023509,S2CID 18393976
- ^Baade, Walter;Swope, Henrietta H. (September 1961), "The Draco system, a dwarf galaxy",The Astronomical Journal,66:300–347,Bibcode:1961AJ.....66..300B,doi:10.1086/108431
- ^Aparicio, Antonio; Carrera, Ricardo; Martínez-Delgado, David (November 2001), "The Star Formation History and Morphological Evolution of the Draco Dwarf Spheroidal Galaxy",The Astronomical Journal,122 (5):2524–2537,arXiv:astro-ph/0108159,Bibcode:2001AJ....122.2524A,doi:10.1086/323535,S2CID 17088564
- ^Mashchenko, Sergey; Sills, Alison; Couchman, H. M. (March 2006), "Constraining Global Properties of the Draco Dwarf Spheroidal Galaxy",The Astrophysical Journal,640 (1):252–269,arXiv:astro-ph/0511567,Bibcode:2006ApJ...640..252M,doi:10.1086/499940,S2CID 18708747
- ^"NASA's Hubble Traces Dark Matter in Dwarf Galaxy Using Stellar Motions". 11 July 2024. Retrieved3 July 2024.
External links
edit
- The Draco Dwarf onWikiSky:DSS2,SDSS,GALEX,IRAS,Hydrogen α,X-Ray,Astrophoto,Sky Map,Articles and images