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NGC5907 (NGC5906, UGC09801), Draco, Knife Edge Galaxy, and Five Quasars
NGC5907 (NGC5906, UGC09801), Draco, Knife Edge Galaxy, and Five Quasars
NGC 5907 is a large nearly edge-on spiral galaxy, first documented by W. Herschel in 1788. On a large scale it is one of the brightest members of the small NGC5866 Galaxy Group in the constellation of Draco. Although the designation generally refers to the entire galaxy, it was not until 1850 that George Stoney identified the faint W part of the galaxy obscured by prominent equatorial dust lanes as NGC 5906. According to NED (NASA Extragalactic Database), the galaxy is 12.8 arcmin in angular size and 9.18 (V) in integrated apparent magnitude Other values found in the literature for the visible band magnitude include 11.12, 11.8, and 12.46, which simply appear too low when compared to the object's photographic brightness. Due to its edge-on orientation its integrated apparent magnitude and the calculated absolute magnitude are significantly underestimated for two reasons. First, it presents to the observer a much smaller surface area than a face-on galaxy. And second, much of its starlight is absorbed and scattered by thick layers of gas and dust in the galactic plane. Its redshift of 0.002225 indicates light travel distance of 30.88 Mly, assuming redshift is due exclusively to the expansion of space (Hubble Flow). For redshifts < 0.01, redshift-independent distance measurements, such as the Cepheid method, are generally more accurate because a fraction of the redshift value is due to an object's motion through space. For NGC5907 the median redshift-independent distance value is 14.275 Mpc, or 46.54 Mly.
Based on the measurable properties, we can estimate NGC5907 to be 172,000 ly in diameter, approximately 40% larger and two times brighter than the Milky Way. Its redshift indicates a recession velocity of 666 km/s. Its morphological classification is SAc (or Sc), indicating a spiral galaxy with loosely wound arms and no evidence of a nuclear bar. Considering the galaxy's nearly edge-on presentation with 87.2* inclination to our line of sight, the presence of a bar can not be confidently ruled out because a view of the nucleus is obscured by dust, gas, and luminous matter in the galactic disk. Garcia-Burillo et al. (1997) suggest that anomalies in molecular gas kinematics can be explained by the presence of a stellar bar. The galaxy has a thin disk with a nearly absent central bulge, resulting in a bulge-to-disk luminosity ratio of only 0.05. Prominent equatorial dust lanes extend nearly to the edges of the galactic disk. While there is some controversy about the presence of extraplanar dust, Xilouris et al. (1999) report that the thickness of extraplanar dust is about 10% larger than the thickness of the stellar disk. As indicated by the light blue floccules of hot newborn stars and by the presence of numerous ionized hydrogen (Hii) regions in the galactic disk, the galaxy displays an above average star formation rate (SFR). This was initially perplexing since the galaxy was thought to be an isolated field spiral with no evidence of tidal disruption. However, deep-sky images by R Jay GaBany (2006) revealed a complex interweaved structure of stellar debris surrounding the galaxy, resulting from an accretion event over four billion years ago. Gravitational perturbations caused by this stream explain elevated SFR and the slight warp in its galactic disk.
www.cosmotography.com/images/small_ring_ngc5907.html
Although it is statistically very likely that NGC5907 contains a central supermassive black hole (SMBH), literature search reveals no information regarding detection of radio wave or high energy emissions from the galactic nucleus. If a central SMBH is present, it shows no evidence of active accretion at this time. Nor can a central SMBH be confirmed by spectroscopy and stellar kinematics. Due to the edge-on orientation, the nucleus is obscured in the optical band by equatorial gas, dust, and luminous matter.
The annotated image indicates the position of an ultra-luminous X-ray source (ULX) within the galaxy's disk. The precise nature of these objects is not confidently known. In order of probability, their energy source is explained as accretion around an intermediate mass black hole (IMBH), super-Eddington accretion around a neutron star or large stellar-mass black holes (BH), or beamed emissions from high mass X-ray binary stars. Pintore et al. (2018) reported an X-ray transient event in this ULX implying a flux increase by a factor of >35. They find the event is consistent with a ~30 solar mass black hole accreting at the Eddington limit, or with beamed emissions from an accreting neutron star.
Other objects of interest on the annotated image include an irregular dwarf galaxy LEDA 54419. Its redshift is very similar to that of NGC5907 suggesting the two might be bound. Distinct blue color indicating high SFR further increases the possibility of tidal interaction. Unfortunately, no redshift-independent distance measurements have been made for this galaxy, and their interaction can not be confirmed. A number of remote galaxies lie in the background. Four of these which carry identifiers are located at distances between 1.6 and 1.73 Bly. Another six even more remote galaxy candidates are marked with letter G. The image also includes five identified quasars. Three of these appear brigher than their listed apparent magnitudes. They are marked with the "+" sign on the chart below. Since quasar luminosity depends on its SMBH accretion rate, quasars often manifest variability up to several magnitudes over a period of days to years. The last two quasars on the list have super-luminal recession velocities in the present cosmological epoch. They have crossed the cosmic event horizon, and the light they are presently emitting can never reach us. The most remote of the quasars is SDSS J151538.77+560520.4 at a light travel distance (lookback time) of 10.86 billion light years.
Image details:
-Remote Takahashi TOA 150 x 1105mm, SBIG STF-8300C, Paramount GT GEM
-OSC 32 x 300 sec, 2x drizzle, 50% linear crop
-Software: DSS, XnView, StarNet++ v2, StarTools v1.3 and 1.8, Cosmological Calculator v3
NGC5907 (NGC5906, UGC09801), Draco, Knife Edge Galaxy, and Five Quasars
NGC5907 (NGC5906, UGC09801), Draco, Knife Edge Galaxy, and Five Quasars
NGC 5907 is a large nearly edge-on spiral galaxy, first documented by W. Herschel in 1788. On a large scale it is one of the brightest members of the small NGC5866 Galaxy Group in the constellation of Draco. Although the designation generally refers to the entire galaxy, it was not until 1850 that George Stoney identified the faint W part of the galaxy obscured by prominent equatorial dust lanes as NGC 5906. According to NED (NASA Extragalactic Database), the galaxy is 12.8 arcmin in angular size and 9.18 (V) in integrated apparent magnitude Other values found in the literature for the visible band magnitude include 11.12, 11.8, and 12.46, which simply appear too low when compared to the object's photographic brightness. Due to its edge-on orientation its integrated apparent magnitude and the calculated absolute magnitude are significantly underestimated for two reasons. First, it presents to the observer a much smaller surface area than a face-on galaxy. And second, much of its starlight is absorbed and scattered by thick layers of gas and dust in the galactic plane. Its redshift of 0.002225 indicates light travel distance of 30.88 Mly, assuming redshift is due exclusively to the expansion of space (Hubble Flow). For redshifts < 0.01, redshift-independent distance measurements, such as the Cepheid method, are generally more accurate because a fraction of the redshift value is due to an object's motion through space. For NGC5907 the median redshift-independent distance value is 14.275 Mpc, or 46.54 Mly.
Based on the measurable properties, we can estimate NGC5907 to be 172,000 ly in diameter, approximately 40% larger and two times brighter than the Milky Way. Its redshift indicates a recession velocity of 666 km/s. Its morphological classification is SAc (or Sc), indicating a spiral galaxy with loosely wound arms and no evidence of a nuclear bar. Considering the galaxy's nearly edge-on presentation with 87.2* inclination to our line of sight, the presence of a bar can not be confidently ruled out because a view of the nucleus is obscured by dust, gas, and luminous matter in the galactic disk. Garcia-Burillo et al. (1997) suggest that anomalies in molecular gas kinematics can be explained by the presence of a stellar bar. The galaxy has a thin disk with a nearly absent central bulge, resulting in a bulge-to-disk luminosity ratio of only 0.05. Prominent equatorial dust lanes extend nearly to the edges of the galactic disk. While there is some controversy about the presence of extraplanar dust, Xilouris et al. (1999) report that the thickness of extraplanar dust is about 10% larger than the thickness of the stellar disk. As indicated by the light blue floccules of hot newborn stars and by the presence of numerous ionized hydrogen (Hii) regions in the galactic disk, the galaxy displays an above average star formation rate (SFR). This was initially perplexing since the galaxy was thought to be an isolated field spiral with no evidence of tidal disruption. However, deep-sky images by R Jay GaBany (2006) revealed a complex interweaved structure of stellar debris surrounding the galaxy, resulting from an accretion event over four billion years ago. Gravitational perturbations caused by this stream explain elevated SFR and the slight warp in its galactic disk.
www.cosmotography.com/images/small_ring_ngc5907.html
Although it is statistically very likely that NGC5907 contains a central supermassive black hole (SMBH), literature search reveals no information regarding detection of radio wave or high energy emissions from the galactic nucleus. If a central SMBH is present, it shows no evidence of active accretion at this time. Nor can a central SMBH be confirmed by spectroscopy and stellar kinematics. Due to the edge-on orientation, the nucleus is obscured in the optical band by equatorial gas, dust, and luminous matter.
The annotated image indicates the position of an ultra-luminous X-ray source (ULX) within the galaxy's disk. The precise nature of these objects is not confidently known. In order of probability, their energy source is explained as accretion around an intermediate mass black hole (IMBH), super-Eddington accretion around a neutron star or large stellar-mass black holes (BH), or beamed emissions from high mass X-ray binary stars. Pintore et al. (2018) reported an X-ray transient event in this ULX implying a flux increase by a factor of >35. They find the event is consistent with a ~30 solar mass black hole accreting at the Eddington limit, or with beamed emissions from an accreting neutron star.
Other objects of interest on the annotated image include an irregular dwarf galaxy LEDA 54419. Its redshift is very similar to that of NGC5907 suggesting the two might be bound. Distinct blue color indicating high SFR further increases the possibility of tidal interaction. Unfortunately, no redshift-independent distance measurements have been made for this galaxy, and their interaction can not be confirmed. A number of remote galaxies lie in the background. Four of these which carry identifiers are located at distances between 1.6 and 1.73 Bly. Another six even more remote galaxy candidates are marked with letter G. The image also includes five identified quasars. Three of these appear brigher than their listed apparent magnitudes. They are marked with the "+" sign on the chart below. Since quasar luminosity depends on its SMBH accretion rate, quasars often manifest variability up to several magnitudes over a period of days to years. The last two quasars on the list have super-luminal recession velocities in the present cosmological epoch. They have crossed the cosmic event horizon, and the light they are presently emitting can never reach us. The most remote of the quasars is SDSS J151538.77+560520.4 at a light travel distance (lookback time) of 10.86 billion light years.
Image details:
-Remote Takahashi TOA 150 x 1105mm, SBIG STF-8300C, Paramount GT GEM
-OSC 32 x 300 sec, 2x drizzle, 50% linear crop
-Software: DSS, XnView, StarNet++ v2, StarTools v1.3 and 1.8, Cosmological Calculator v3