اشترك بالحزمة الذهبية واحصل على وصول غير محدود شمرا أكاديميا
تسجيل مستخدم جديدDiscovery of a close pair of faint dwarf galaxies in the halo of Centaurus A
118
0
0.0
(
0
)
تأليف
D. Crnojevic
اسأل ChatGPT حول البحث
ﻻ يوجد ملخص باللغة العربية
As part of the Panoramic Imaging Survey of Centaurus and Sculptor (PISCeS) we report the discovery of a pair of faint dwarf galaxies (CenA-MM-Dw1 and CenA-MM-Dw2) at a projected distance of $sim$90 kpc from the nearby elliptical galaxy NGC5128 (CenA). We measure a tip of the red giant branch distance to each dwarf, finding $D=3.63 pm 0.41$ Mpc for CenA-MM-Dw1 and $D=3.60 pm 0.41$ Mpc for CenA-MM-Dw2, both of which are consistent with the distance to NGC5128. A qualitative analysis of the color magnitude diagrams indicates stellar populations consisting of an old, metal-poor red giant branch ($gtrsim 12$ Gyr, [Fe/H]$sim-1.7$ to -1.9). In addition, CenA-MM-Dw1 seems to host an intermediate-age population as indicated by its candidate asymptotic giant branch stars. The derived luminosities ($M_V=-10.9pm0.3$ for CenA-MM-Dw1 and $-8.4pm0.6$ for CenA-MM-Dw2) and half-light radii ($r_{h}=1.4pm0.04$ kpc for CenA-MM-Dw1 and $0.36pm0.08$ kpc for CenA-MM-Dw2) are consistent with those of Local Group dwarfs. CenA-MM-Dw1s low central surface brightness ($mu_{V,0}=27.3pm0.1$ mag/arcsec$^2$) places it among the faintest and most extended M31 satellites. Most intriguingly, CenA-MM-Dw1 and CenA-MM-Dw2 have a projected separation of only 3 arcmin ($sim3$ kpc): we are possibly observing the first, faint satellite of a satellite in an external group of galaxies.
قيم البحث
اقرأ أيضاً
The Panoramic Imaging Survey of Centaurus and Sculptor (PISCeS) is constructing a wide-field map of the resolved stellar populations in the extended halos of these two nearby, prominent galaxies. We present new Magellan/Megacam imaging of a $sim3$ de
g$^2$ area around Centaurus A (Cen A), which filled in much of our coverage to its south, leaving a nearly complete halo map out to a projected radius of $sim$150 kpc and allowing us to identify two new resolved dwarf galaxies. We have additionally obtained deep Hubble Space Telescope (HST) optical imaging of eleven out of the thirteen candidate dwarf galaxies identified around Cen A and presented in Crnojevic et al. (2016): seven are confirmed to be satellites of Cen A, while four are found to be background galaxies. We derive accurate distances, structural parameters, luminosities and photometric metallicities for the seven candidates confirmed by our HST/ACS imaging. We further study the stellar population along the $sim$60 kpc long (in projection) stream associated with Dw3, which likely had an initial brightness of $M_{V}$$sim$$-$15 and shows evidence for a metallicity gradient along its length. Using the total sample of eleven dwarf satellites discovered by the PISCeS survey, as well as thirteen brighter previously known satellites of Cen A, we present a revised galaxy luminosity function for the Cen A group down to a limiting magnitude of $M_Vsim-8$, which has a slope of $-1.14pm0.17$, comparable to that seen in the Local Group and in other nearby groups of galaxies.
We present deep Hubble Space Telescope imaging of five faint dwarf galaxies associated with the nearby spiral NGC 253 (D$approx$3.5 Mpc). Three of these are newly discovered ultra-faint dwarf galaxies, while all five were found in the Panoramic Imagi
ng Survey of Centaurus and Sculptor (PISCeS), a Magellan$+$Megacam survey to identify faint dwarfs and other substructures in resolved stellar light around massive galaxies outside of the Local Group. Our HST data reach $gtrsim$3 magnitudes below the tip of the red giant branch for each dwarf, allowing us to derive their distances, structural parameters, and luminosities. All five systems contain predominantly old, metal-poor stellar populations (age$sim$12 Gyr, [M/H]$lesssim$$-$1.5) and have sizes ($r_{h}$$sim$110-3000 pc) and luminosities ($M_V$$sim$$-7$ to $-12$ mag) largely consistent with Local Group dwarfs. The three new NGC 253 satellites are among the faintest systems discovered beyond the Local Group. We also use archival HI data to place limits on the gas content of our discoveries. Deep imaging surveys such as our program around NGC 253 promise to elucidate the faint end of the satellite luminosity function and its scatter across a range of galaxy masses, morphologies, and environments in the decade to come.
We report the photometric properties of 16 dwarf galaxies, 15 of which are newly identified, in the Western halo of the nearby giant elliptical galaxy NGC5128. All candidates are found at projected distances $sim!100!-!225$kpc from their giant host,
with luminosities $-10.82!leq!M_V/{rm mag}!leq!-7.42$ and effective radii $4!leq!r_{rm eff}!leq!17$ (or $75!leq!r_{rm eff}/{rm pc}!leq!300$ at the distance of NGC5128). We compare to other low-mass dwarf galaxies in the local universe and find them to populate the faint/compact extension of the size-luminosity relation that was previously not well-sampled by dwarf galaxies in the Centaurus A system, with optical colors similar to compact stellar systems like globular clusters and ultra-compact dwarf galaxies despite having much more diffuse morphologies. From optical $ugriz$ photometry, stellar masses are estimated to be $5.17!leq!log{cal M}_star/M_odot!leq!6.48$, with colors that show them to fall redward of the dwarf galaxy mass-metallicity relation. These colors suggest star formation histories that require some mechanism that would give rise to extra metal enrichment such as primordial formation within the halos of their giant galaxy hosts, non-primordial star formation from previously enriched gas, or extended periods of star formation leading to self-enrichment. We also report the existence of at least two sub-groups of dwarf candidates, each subtending $10-20$ on the sky, corresponding to projected physical separations of $10!-!20$kpc. True physical associations of these groups, combined with their potentially extended star formation histories, would imply that they may represent dwarf galaxy groups in the early stage of interaction upon infall into a giant elliptical galaxy halo in the very nearby universe.
While theoretical arguments predict that most of the early growth of supermassive black holes (SMBHs) happened during heavily obscured phases of accretion, current methods used for selecting $z>6$ quasars (QSOs) are strongly biased against obscured Q
SOs, thus considerably limiting our understanding of accreting SMBHs during the first Gyr of the Universe from an observational point of view. We report the $Chandra$ discovery of the first heavily obscured QSO candidate in the early universe, hosted by a close ($approx5$ kpc) galaxy pair at $z=6.515$. One of the members is an optically classified type 1 QSO, PSO167-13. The companion galaxy was first detected as a [C II] emitter by ALMA. An X-ray source is significantly ($P=0.9996$) detected by $Chandra$ in the 2-5 keV band, with $<1.14$ net counts in the 0.5-2 keV band, although the current positional uncertainty does not allow a conclusive association with either PSO167-13 or its companion galaxy. From X-ray photometry and hardness-ratio arguments, we estimated an obscuring column density of $N_H>2times10^{24},mathrm{cm^{-2}}$ and $N_H>6times10^{23},mathrm{cm^{-2}}$ at $68%$ and $90%$ confidence levels, respectively. Thus, regardless of which of the two galaxies is associated with the X-ray emission, this source is the first heavily obscured QSO candidate at $z>6$.
We report the discovery of 158 previously undetected dwarf galaxies in the Fornax cluster central regions using a deep coadded $u, g$ and $i$-band image obtained with the DECam wide-field camera mounted on the 4-meter Blanco telescope at the Cerro To
lolo Interamerican Observatory as part of the {it Next Generation Fornax Survey} (NGFS). The new dwarf galaxies have quasi-exponential light profiles, effective radii $0.1!<!r_e!<!2.8$ kpc and average effective surface brightness values $22.0!<!mu_i!<!28.0$ mag arcsec$^{-2}$. We confirm the existence of ultra-diffuse galaxies (UDGs) in the Fornax core regions that resemble counterparts recently discovered in the Virgo and Coma galaxy clusters.~We also find extremely low surface brightness NGFS dwarfs, which are several magnitudes fainter than the classical UDGs. The faintest dwarf candidate in our NGFS sample has an absolute magnitude of $M_i!=!-8.0$,mag. The nucleation fraction of the NGFS dwarf galaxy sample appears to decrease as a function of their total luminosity, reaching from a nucleation fraction of $>!75%$ at luminosities brighter than $M_i!simeq!-15.0$ mag to $0%$ at luminosities fainter than $M_i!simeq!-10.0$ mag. The two-point correlation function analysis of the NGFS dwarf sample shows an excess on length scales below $sim!100$ kpc, pointing to the clustering of dwarf galaxies in the Fornax cluster core.
سجل دخول لتتمكن من نشر تعليقات
التعليقات
جاري جلب التعليقات
سجل دخول لتتمكن من متابعة معايير البحث التي قمت باختيارها
