M94 (NGC 4736)
A beautifully clear night (marred only a bright full moon) allowed us to image an object we haven't tried before...M94 (sometimes called the Croc's Eye Galaxy). I was intrigued at first by the ring surrounding it but it turns out that this galaxy has some other mysteries.
[From Wikipedia] Messier 94 (also known as NGC 4736) is a spiral galaxy approximately 16 million light-years away in the constellation Canes Venatici. It is one of the brightest galaxies of the M94 group which is part of the Virgo Supercluster of galaxies. Although some references describe M94 as a barred spiral galaxy, the "bar" structure appears to be more oval-shaped. The galaxy has two ring structures, an inner ring with a diameter of 70 arcseconds and an outer ring with a diameter of 600 arcseconds (about 45,000 light-years). These rings appear to form at resonance points in the disk of the galaxy. The inner ring is the site of strong star formation activity and is sometimes referred to as a starburst ring. This star formation is fueled by gas driven dynamically into the ring by the inner oval-shaped bar-like structure. A 2009 study conducted by an international team of astrophysicists revealed that the outer ring of M94 is not a closed stellar ring but a complex structure of spiral arms when viewed in mid-IR and UV. The study found that the outer disk of this galaxy is active. It contains approximately 23% of the galaxy's total stellar mass and contributes about 10% of the galaxy's new stars. In fact, the star formation rate of the outer disk is approximately two times greater than the inner disk because it is more efficient per unit of stellar mass. The report concluded that the inner disk of M94 is an oval distortion which led to the creation of this galaxy's peripheral disk.
In 2008 a study was published showing that M94 had very little or no dark matter present. The study analyzed the rotation curves of the galaxy's stars and the density of hydrogen gas and found that ordinary luminous matter appeared to account for all of the galaxy's mass. This result was unusual and somewhat controversial, as current models do not indicate how a galaxy could form without a dark matter halo or how a galaxy could lose its dark matter. Other explanations for galactic rotation curves, such as MOND, also have difficulty explaining this galaxy. This result has yet to be confirmed or accepted by other research groups, however, and has not actually been tested against the predictions of standard galaxy formation models.
18-19/03/2022
036 x 300-second exposures at Unity Gain (139) cooled to -10°C
055 x dark frames
040 x flat frames
100 x bias frames
Binning 1x1
Total integration time = 3 hours
Captured with APT
Guided with PHD2
Processed in Nebulosity and Photoshop
Equipment:
Telescope: Sky-Watcher Explorer-150PDS
Mount: Skywatcher EQ5
Guide Scope: Orion 50mm Mini
Guiding Camera: SVBONY SV105 with ZWO USBST4 guider adapter
Imaging Camera: ZWO ASI1600MC Pro with anti-dew heater
Baader Mark-III MPCC Coma Corrector
Filter: Optolong L-Pro
M94 (NGC 4736)
A beautifully clear night (marred only a bright full moon) allowed us to image an object we haven't tried before...M94 (sometimes called the Croc's Eye Galaxy). I was intrigued at first by the ring surrounding it but it turns out that this galaxy has some other mysteries.
[From Wikipedia] Messier 94 (also known as NGC 4736) is a spiral galaxy approximately 16 million light-years away in the constellation Canes Venatici. It is one of the brightest galaxies of the M94 group which is part of the Virgo Supercluster of galaxies. Although some references describe M94 as a barred spiral galaxy, the "bar" structure appears to be more oval-shaped. The galaxy has two ring structures, an inner ring with a diameter of 70 arcseconds and an outer ring with a diameter of 600 arcseconds (about 45,000 light-years). These rings appear to form at resonance points in the disk of the galaxy. The inner ring is the site of strong star formation activity and is sometimes referred to as a starburst ring. This star formation is fueled by gas driven dynamically into the ring by the inner oval-shaped bar-like structure. A 2009 study conducted by an international team of astrophysicists revealed that the outer ring of M94 is not a closed stellar ring but a complex structure of spiral arms when viewed in mid-IR and UV. The study found that the outer disk of this galaxy is active. It contains approximately 23% of the galaxy's total stellar mass and contributes about 10% of the galaxy's new stars. In fact, the star formation rate of the outer disk is approximately two times greater than the inner disk because it is more efficient per unit of stellar mass. The report concluded that the inner disk of M94 is an oval distortion which led to the creation of this galaxy's peripheral disk.
In 2008 a study was published showing that M94 had very little or no dark matter present. The study analyzed the rotation curves of the galaxy's stars and the density of hydrogen gas and found that ordinary luminous matter appeared to account for all of the galaxy's mass. This result was unusual and somewhat controversial, as current models do not indicate how a galaxy could form without a dark matter halo or how a galaxy could lose its dark matter. Other explanations for galactic rotation curves, such as MOND, also have difficulty explaining this galaxy. This result has yet to be confirmed or accepted by other research groups, however, and has not actually been tested against the predictions of standard galaxy formation models.
18-19/03/2022
036 x 300-second exposures at Unity Gain (139) cooled to -10°C
055 x dark frames
040 x flat frames
100 x bias frames
Binning 1x1
Total integration time = 3 hours
Captured with APT
Guided with PHD2
Processed in Nebulosity and Photoshop
Equipment:
Telescope: Sky-Watcher Explorer-150PDS
Mount: Skywatcher EQ5
Guide Scope: Orion 50mm Mini
Guiding Camera: SVBONY SV105 with ZWO USBST4 guider adapter
Imaging Camera: ZWO ASI1600MC Pro with anti-dew heater
Baader Mark-III MPCC Coma Corrector
Filter: Optolong L-Pro