We present HST/STIS spectra of the Sbc spiral galaxy NGC 4041 which were used to map the velocity field of the gas in its nuclear region .
We detect the presence of a compact ( r \simeq 0 \farcs 4 \simeq 40 \mathrm { ~ { } pc } ) , high surface brightness , rotating nuclear disk co-spatial with a nuclear star cluster .
The disk is characterized by a rotation curve with a peak to peak amplitude of \sim 40 \mathrm { ~ { } km } \mathrm { ~ { } s } ^ { -1 } and is systematically blueshifted by \sim 10 - 20 \mathrm { ~ { } km } \mathrm { ~ { } s } ^ { -1 } with respect to the galaxy systemic velocity .
With the standard assumption of constant mass-to-light ratio and with the nuclear disk inclination taken from the outer disk , we find that a dark point mass of ( 1 _ { -0.7 } ^ { +0.6 } ) \times 10 ^ { 7 } ~ { } \mathrm { M } _ { \odot } is needed to reproduce the observed rotation curve .
However the observed blueshift suggests the possibility that the nuclear disk could be dynamically decoupled .
Following this line of reasoning we relax the standard assumptions and find that the kinematical data can be accounted for by the stellar mass provided that either the central mass-to-light ratio is increased by a factor of \sim 2 or that the inclination is allowed to vary .
This model results in a 3 \sigma upper limit of 6 \times 10 ^ { 6 } ~ { } \mathrm { M } _ { \odot } on the mass of any nuclear black hole .
Overall , our analysis only allows us to set an upper limit of 2 \times 10 ^ { 7 } ~ { } \mathrm { M } _ { \odot } on the mass of the nuclear \mathrm { BH } .
If this upper limit is taken in conjunction with an estimated bulge B magnitude of -17.7 and with a central stellar velocity dispersion of \simeq 95 \mathrm { ~ { } km } \mathrm { ~ { } s } ^ { -1 } , then these results are not inconsistent with both the M _ { \mathrm { BH } } - L _ { \mathrm { sph } } and the M _ { \mathrm { BH } } - \sigma _ { \star } correlations .
Constraints on \mathrm { BH } masses in spiral galaxies of types as late as Sbc are still very scarce and therefore the present result adds an important new datapoint to our understanding of \mathrm { BH } demography .